THE PICTURE OF THE FUTURE
The Bell System is about to add PICTURE-
PHONE® service to the many services it now of-
fers customers. A major trial of a Picturephone
system is presently under way, and commercial
service is scheduled for mid 1970. Because Pic-
turephone service is a large undertaking that will
have a profound effect on communications, the
RECORD is pleased to be able to present this special
issue describing the new system for our readers.
Special issues have become an important part
of the RECORD's continuing story of science and
technology at Bell Labs. The first one, in June
1958, dealt with the transistor and marked the
tenth anniversary of its invention at Bell Labs.
Since then there have been special issues on the
TELSTAR® project, No. 1 Ess, and integrated elec-
tronics. In addition, there have been single-topic
issues devoted to the N-3 and L-4 carrier trans-
mission systems. We hope to continue to present
such special issues from time to time as a way of
highlighting subjects of special importance.
134 P ICTUREPHONE Service-A New Way of Communicating
An introduction by Julius P. Molnar, Executive Vice President, Bell Telephone
136 P ICTUREPHONE Irwin Dorros
A broad view of the PICTUREPHONE system sets the stage for the more detailed
discussions that f ollow.
142 Getting the Picture C. G. Davis
The acceptance of PICTUREPHONE service depends largely on the equipment that
people will see and use-the PICTUREPHONE set itself.
148 Video Service for Business J. R. Harris and R. D. Williams
A look at how PICTUREPHONE service will be added to existing business telephone
154 Choosing the Route F. A. Korn and A. E. Ritchie
A proven Bell System performer, No. 5 crossbar, will be the nucleus for switching
a brand-new communications service.
160 The Evolution of PICTUREPHONE Service
Photos highlighting some important dates and events that have led up to the
system described in this issue.
162 Transmission Across Town or Across the Country
D. W. Nast and I. Welber
Digital transmission is the key to plans for transmitting high-quality PICTURE-
PHONE signals over almost unlimited distances.
169 Connecting the Customer F. T. Andrews, Jr., and H. Z. Hardaway
The continually-evolving customer loop plant is adding a new capability to its com-
munications repertoire-video transmission.
174 Devices-The Hardware of Progress S. O. Ekstrand
PICTUREPHONE service would not be possible without the electronic devices that
modern technology has produced.
181 Maintenance-Keeping the System in Trim A. E. Spencer
A description of some of the equipment and procedures that will be used to main-
tain the PICTUREPHONE system.
Some of the things Bell Labs is doing now to make the PICTUREPHONE system an
even better, more versatile instrument for human communication.
188 The Authors
A New Way of Communicating
An Introduction by Julius P. Molnar, Executive Vice President, Bell Telephone Laboratories
Rarely does an individual or an organization have an opportunity to create
something of broad utility that will enrich the daily lives of everybody.
Alexander Graham Bell with his invention of the telephone in 1876, and the
various people who subsequently developed it for general use, perceived such
an opportunity and exploited it for the great benefit of society. Today there
stands before us an opportunity of equal magnitude- PICTUREPHONE® service.
F IFTY YEARS AGO people communicated
over distances mainly by letters and tele-
out being self-conscious, he senses in his con-
versation an enhanced feeling of proximity
grams, and used streetcars, railroads, and and intimacy with the other party. The uncon-
ships for travel to see each other. Gradually scious response that party makes to a remark
telephone usage increased until it is today the by breaking into a smile, or by dropping his
most common means of communication, and jaw, or by not responding at all, adds a defi-
the automobile and jet airplane now provide nite though indescribable "extra" to the com-
most of the transportation we use to get to- munication process. Regular users of Picture-
gether for face-to-face conversation. I predict phone over the network between BTL and
that before the turn of the century Picture- AT&T's headquarters building have agreed
phone will similarly displace today's means of that conversations over Picturephone convey
communication, and in addition will make much important information over and above
many of today's trips unnecessary. that carried by the voice alone. Clearly, "the
The urge to travel and see the world with next best thing to being there" is going to be
one's own eyes will probably be enhanced, a Picturephone call.
not lessened, by the availability of instant, Real person-to-person conversation is still
personal picture communications; but the man's most complete and satisfying way of
need for many ordinary trips for shopping, communicating. Letters and other written
for conducting normal business, and for some forms of expression have their values, but
social purposes should be greatly reduced. As they suffer from two disadvantages. They are
a result, there will be less need for dense pop- essentially one-way communications, and with
ulation centers. We can even hope to see an written words it is difficult to convey mean-
end to the continuing increase in city traffic ings beyond their strict lexical definitions.
and traffic jams. The telephone overcomes one of these dis-
Picturephone is therefore much more than advantages because it permits a two-way,
just another means of communication. It may give-and-take interchange of information and
in fact help solve many social problems, ideas. It partially overcomes the second dis-
particularly those pertaining to life in the big advantage also, because in addition to the
city. Bringing Picturephone into general use literal meanings of words, one can-with
I see as one of the most exciting opportunities voice tone, volume and inflection-convey
for the wise use of modern technology. many of the additional elements of a complete
Most people when first confronted with Pic- communication.
turephone seem to imagine that they will use For the final, visual elements of two-way
it mainly to display objects or written matter, communication, we have had to rely on visits,
or they are very much concerned with how meetings, and conferences. Even here there
they will appear on the screen of the called is a disadvantage, however. Such communi-
party. These reactions are only natural, but cation is at its best only when the participants
they also indicate how difficult it is to predict are within about ten feet of each other. Be-
the way people will respond to something new yond this distance, face-to-face communica-
and different. tion quickly becomes unsatisfactory. Just as
Those of us who have had the good fortune the telegraph overcame this distance barrier
to use Picturephone regularly in our daily for written words, and the telephone for
communications find that although it is use- spoken words, so Picturephone service will
ful for displaying objects or written matter, bring people face-to-face across our contin-
its chief value is the face-to-face mode of com- ent and eventually over oceans.
munication it makes possible. Once the novelty ( For concluding remarks and a look into the
wears off and one can use Picturephone with- future of Picturephone service, see p. 186.)
May/June 1969 135
T HE TELEPHONE brought a new dimension to hu-
man communications. Where previously men
had been able to send written messages over wires
The equipment at the Picturephone custom-
er's location consists of four parts: a 12-button
Touch-Tone telephone; a display unit, with pic-
as electrical signals, the telephone made it pos- ture tube, camera tube, and a loudspeaker built
sible for the human voice to span the miles. Now, in; a control unit, which contains a microphone;
almost a hundred years later, the telephone is and a service unit containing power supply, logic
commonplace and another dimension is being circuits, and transmission equalizing circuits,
added-that of sight. And just as the telephone which is installed out of sight.
has revolutionized human habits of communicat- Picture standards have been chosen for the best
ing and made a major contribution to the quality possible picture, subject to the limits imposed by
of modern life, many of us at Bell Labs believe cost and transmission capabilities (see the table on
that PICTUREPHONE® service, the service that lets page 139). The picture signal is composed of
people see as well as hear each other, offers about 250 active lines, displayed 30 times per sec-
potential benefits to mankind of the same magni- ond on a 5.5 -inch by 5-inch screen. Resolution is
tude. It is a tribute to the flexibility and versatility the same in the vertical and horizontal directions.
of the existing telephone network that Picture- The quality of the picture equals that of a typical
phone service, now being readied for introduction television set in the home. Transmitting the pic-
as a regular Bell System offering, can be added ture signal requires a 1-MHz bandwidth.
as an integral part of telephone service. Normally, a person using the Picturephone set
What is Picturephone service like? Most im- will be about 36 inches away from the screen. The
portant, of course, the user sees the person with field of view at that distance is adjustable from
whom he is talking. People today are so accus- 17.5-by-16 inches to 28.5 -by-26 inches. This
tomed to using the telephone and to its usefulness range of sizes is designed to give the user free-
as an instrument of communication, that they dom to move from side to side during his conver-
sometimes overlook the importance of vision in sation, and to permit one or two other persons to
communication. But think, do you telephone the be "on camera" at the same time. The camera iris
person in the next office or go to see him? Most automatically adjusts the lens for changes in
people sense a more complete and satisfying ex- room lighting.
change when they can both see and talk to each The Picturephone system is designed to take
other. Thus, the advantage of more complete com- maximum advantage of the existing telephone
munication with Picturephone service is readily network and add as little new equipment as pos-
apparent. sible. Picturephone customers will make voice-
Picturephone service is useful in other ways only telephone calls from their regular telephones,
too. Graphic material, such as drawings, photo- with all extra features, such as speakerphone,
graphs, and physical objects, can be viewed with card dialers, and key telephone options, in place.
the Picturephone set. The equipment can also be A 12-button Touch-Tone telephone set will be
used to communicate with a computer. The cus- required for Picturephone service (all Touch-
tomer "talks" to the computer via TOUCH-TONE@ Tone phones are now being manufactured with 12
dialing buttons, and the computer's responses are buttons). The Picturephone customer initiates
displayed on the picture tube (see Picturephone a video call by pressing the lower right-hand, or
Sets Put a Computer on Executive Desks, REC - 12th button, labeled #, and then, in most cases,
ORD, June 1968). dials the regular telephone number of the person
When Picturephone service becomes available he is calling.
commercially (in the early 1970's), it will prob- A distinctive ring, created by a new tone
ably be accepted most readily by businesses-par- ringer, identifies an incoming Picturephone call.
ticularly by large corporations. The executives of In key telephones, such as a six-button set, the
a corporation with offices in different locations key corresponding to the called line lights red to
form a natural "community" with a need for the identify a Picturephone call; the key lights
utmost in communication facilities. Trials already white to identify a voice-only telephone call.
conducted and now in progress have demonstrated Lines equipped for Picturephone service can
the usefulness of Picturephone service in the also have voice-only extensions-a secretary's
corporate environment (see The Evolution of Pic- pickup, for example. Video calls can be answered
turephone Service, RECORD, October 1968). As on such extensions; the caller sees a blank screen
Picturephone service becomes widely available until the call is answered on a Picturephone set.
and a public awareness of it develops, it will An attendant at a PBX, for example, may or may
spread gradually into the residential market. not be equipped for picture service, as the cus-
138 Bell Laboratories Record
tomer wishes. In addition, at the customer's op-
tion a fixed image, such as a company trademark,
can be transmitted to the caller while the atten-
dant handles the call.
Communication services available to the busi-
ness community today range from simple direct
lines to PBX and centrex arrangements for busi-
ness customers. Individual service features in-
clude dial intercommunication, attendant service,
and, in the case of centrex, direct inward dialing
to telephones and identified outward dialing, as
well as a variety of sophisticated services tailored
to meet specific needs.
Picturephone service will be a valuable addi-
tion to the telephone services already available to
business. To assure continuation of these services,
new Picturephone key telephone units offering
pickup, hold, and intercom service will be fur-
nished. Customers served by the 701 and 757
PBX's, the No. 101 ESS, and the No. 5 crossbar
centrex-CO (switched in the central office) sys-
tems will be able to add Picturephone service
and retain all of their major PBX and centrex fea-
tures. Picturephone service with the No. 1 Ess
centrex-CO system and other new PBX systems
will be introduced later.
Thus far, our discussion has related primarily
to Picturephone service as it will affect the user. tomers served from step-by-step, panel, or No. 1
What about the rest of the system? Here too the crossbar offices will be routed to a nearby No. 5
philosophy of taking maximum advantage of ex- crossbar or, later, a No. 1 ESS office.
isting telephone facilities prevails. The upper Whenever a customer dials a call, the common
diagram on page 140 shows the basic local equip- control equipment in the switching machine recog-
ment arrangement. nizes the digits and causes a talking path to be
Picturephone service requires no modifications established. For voice-only calls, the existing two-
to existing two-wire loops (the wires that con- wire telephone switch will make the connection.
nect a customer's telephone to the local switching When the special prefix, #, is dialed, indicating a
office) ; voice-only calls and the voice portion of Picturephone call, the talking path is established
Picturephone calls use these wires. Two more by the two-wire telephone switch, and a path is
pairs of wires in standard telephone cables are established simultaneously by the four-wire video
assigned for the picture signals, one pair for switch to the trunk side of the switching machine.
transmission in each direction. Equalizers are in- There, the audio and video paths form a compos-
serted at about one-mile intervals along the addi- ite six-wire appearance. For intra-office calls, the
tional pairs. The ON-OFF switch-hook signals and six-wire Picturephone signal returns through the
Touch-Tone dialing signals, as well as the voice switches to another line. For calls to a distant cen-
portion of Picturephone calls, are transmitted tral office, however, the path is established over a
over the voice pair. six-wire Picturephone trunk. The audio portion
At the local central office, the voice pair is con- of the six-wire trunk is never used for voice-only
nected to the existing telephone switch in the telephone traffic.
conventional way. The video pairs, however, are The Picturephone signal discussed thus far
connected to a separate four-wire video switch is a line-by-line electrical representation of the
under the control of the existing telephone switch- scanned shades of gray,in the picture material.
ing machine. Short synchronizing pulses, between scan lines
As Picturephone service is first offered, No. 5 and fields, tell the receivers how to line up the parts
crossbar switching machines will be modified to of images. This kind of signal is called "analog."
switch video calls; the capability will be added Between central offices, up to about six miles
to No. 1 ESS later. Picturephone service for cus- apart, the picture signal is transmitted over the
May/June 1969 1 39
signal. Once encoded, a signal usually is not de-
coded until it is within six miles of the distant
local central office. Limitation to a single encoding
in a connection is required to prevent an accum-
ulation of the picture degradation that occurs
each time the signal is coded and decoded. While
some impairment is caused by the single coding
and decoding, digital transmission is highly de-
The customer's Picturephone set is connected to the local cen- sirable because virtually no further impairment
tral office over a six-wire loop. As in today's telephone service, occurs during the transmission of the digital
one pair of wires carries the voice signal. Two other pairs with pulse streams.
equalizers are used for the two directions of video transmission. Picturephone signals remain in digital form
The audio pair is switched in the central office in the conven- for switching in toll offices. No. 5 crossbar switch-
tional way, while the video portion is switched by a newly de- ing offices will be the first to perform the toll
signed four-wire video switch controlled by the switching ma- switching function. Later electronic toll centers
chine. The entire Picturephone signal is switched to other now being planned will switch Picturephone calls.
central offices over a special six-wire trunk; voice-only calls The application of analog and digital transmis-
continue to be switched over conventional two-wire trunks. sion is shown below left. The T-2 digital carrier
system, expected to be introduced in the near fu-
ture, transmits at 6.3 Mb/s and is, in fact, the
reason for selecting this particular signal encod-
ing rate for Picturephone signals. The T-2 system
operates over wire pairs for distances up to sev-
eral hundred miles.
Digital transmission systems now being de-
veloped will ultimately take over the long-haul
transmission of Picturephone signals. Until then,
two existing facilities will be used: the TD-2 mi-
crowave radio relay system and the L-4 carrier
system. In TD-2, a 20-Mb/s pulse stream, carry-
ing three coded Picturephone signals, is trans-
mitted on a single radio channel. In the L-4
system, a 13-Mb/s pulse stream, carrying two
coded Picturephone signals, is transmitted in
place of one of the six mastergroups on a coaxial
tube. No additional transmission facilities, other
than the designs now existing or contemplated for
regular telephone service, will be necessary to
transmit Picturephone signals. A single trans-
mission network will transmit all services.
The Picturephone signal is transmitted between nearby cen- The picture that is finally viewed at a Picture-
tral offices (less than six miles) in analog form (top). For phone receiver contains impairments introduced
transmission beyond six miles, the picture signal and the audio by each part of the built-up connection. Just as in
and signaling information are digitally encoded into a com- today's telephone network, the end-to-end impair-
posite 6.3-Mb/ s signal and decoded again at the distant office. ments are controlled by holding each part of the
connection within specified limits. Based on an-
alytical calculations and subjective tests, each of
Picturephone trunk in analog form. The Picture- these has been assigned a numerical end-to-end
phone trunk in this case consists of three separate maximum value with a specified limit allocated
wire pairs in exchange cables, with equalizers to stations, loops, trunks, etc. Dealing with these
placed at about one-mile spacing in the two video i mpairments requires techniques that are, in many
pairs, as in loops. cases, different from those used for audio trans-
For transmission beyond six miles, the picture, mission systems. The necessary new techniques
voice, and interoffice signal information is digitally are being developed.
encoded into a composite pulse stream of 6.3 meg- The switched network arrangements for Pic-
abits per second (Mb/s). This is called a "digital" turephone service will be useful for services in
1 40 Bell Laboratories Record
addition to Picturephone calling. Equipment will
be developed that, to the network, looks like a Pic-
turephone set, but is actually a data set. A cus-
tomer will be able to dial the data set, using
a regular Picturephone number, and reach a com-
puter. The Touch-Tone dial will then be the means
of communicating with the computer to retrieve
data or interact in a computation. (One kind of
computer response is shown in the upper photo-
graph on this page.)
The network will also be equipped to handle
machine-to-machine data traffic at a rate of about
one Mb/s, much as DATA-PHONE® service handles
voice-band data. Such service will require an ap-
propriate data set at each end of a connection.
To verify the practicality of the Picturephone
system plan, to make refinements in it, and to test
customer acceptance of the features, a product
trial was begun in February of this year and is
still in progress. A total of 41 sets have been
placed in offices of the Westinghouse Electric
Corporation in Pittsburgh and New York with toll
links between cities. Each set can be dialed from
any other set, and computer access facilities are
included in this trial. Acceptance by the users
has been enthusiastic.
Many readers will be led to speculate about
possibilities for future improvements. Among the
items currently receiving attention are higher
resolution for transmitting detailed documents,
color, capability for making conferences calls, and
reducing the transmission band by taking advan-
tage of inherent redundancy in video images.
Satisfactory transmission of a stationary im-
age, such as a drawing resting on a table, does
not require 30 frames per second. In theory an im-
age may be slowly scanned a few times per sec-
ond with many lines, resulting in higher-resolution
transmission within the same 1-MHz channel.
Optional equipment arrangements to achieve this
are now being investigated.
A sizable fundamental research effort is now
in progress to gain enough understanding to pro-
pose a compatible color system for future phases
of the service.
For Picturephone conference calling, an ex-
periment is now in progress in which a voice-
actuated switch causes the picture of the person Besides the "see-as-you-talk" capability of the Picturephone
talking to appear on the screens of all other con- set, man can communicate with a computer as well. A data set,
ferees. Finally, a number of signal-processing which appears to the switched network as a regular Picture-
approaches which may reduce the 6.3-Mb/s rate phone set, permits the set to be connected to a commercial
of transmission are in the research stages. computer. In this case, the Touch-Tone dial is used to communi-
A practical beginning has been made. Develop- cate with the computer and the information retrieved or the
ment of Picturephone service to its present stage results of a computation can be displayed on the Picturephone
brings the goal of better, more natural, and more screen. The variety of characters available to display informa-
nearly complete communications nearer to reality. tion on the Picturephone screen is shown in the bottom photo.
The greatest technical accomplishment in the world may go unused if it is not designed
with people in mind. Thus, the parts of the Picturephone system that people will use
directly have been designed to be attractive, easy to operate, reliable, and versatile.
Getting the Picture
C. G. Davis
EOPLE'S REACTIONS to PICTUREPHONE® service into a successful Picturephone system. In 1965,
will be based largely on the unit that displays a significant milestone in the evolution of Pic-
the picture, along with accompanying controls turephone service was the beginning of product
and other items in the customer's home or office. trials, using what was called the "Mod I" Pic-
Is the equipment attractive? Functional? Reli- turephone set. The results of these trials were
able? Is it easy to use? Is the picture good? Com- then used to develop the latest and completely
ing up with the right answers to these and sim- new Picturephone set, known as the Mod II.
ilar questions has been a major concern at Bell The Mod II set consists of a picture display
Labs as the Picturephone system has evolved. unit (containing the camera, picture tube, and
The "right answers" means, first of all, that the loudspeaker), a control unit (containing the con-
picture itself must be clear and sharp and must trol buttons and knobs and a microphone), a 12-
stay that way without a lot of tuning adjust- button TOUCH-TONE® telephone, and a service
ments. The equipment must be easy to operate. The unit (containing the power supply, logic circuits,
camera must adapt readily to a variety of picture and transmission equalizing circuits). The first
subjects, backgrounds, and lighting conditions. three units are color-coordinated and intended to
At the same time, the set must be versatile fit in as harmoniously as possible with any decor,
enough to meet diverse needs such as showing since they will almost always be in plain sight.
sketches or objects, changing the field of view, The service unit is intended to be installed out of
or allowing the person using it to turn off the sight and can be up to 85 feet away from the
camera if he doesn't want to be seen. The user other three.
should be able to select any of these modes easily The display unit is mounted on a sculptured
and conveniently, with little need for thought or ring stand and can be turned almost all the way
chance of error. Finally, the set, like all Bell Sys- around (340 degrees)
tem equipment, must be designed for a long life on the stand. Since
of trouble-free service under the hazards of the ring stand has
everyday use. a "non-skid" base,
These objectives, and the knowledge gained the unit is not eas-
from study and experimentation over the past 10 ily pushed or pulled
years (see The Evolution of Picturephone Ser- off the surface on
vice, RECORD, October 1968), have helped shape which it rests. How-
technical possibilities and customer preferences ever, when the unit
is tilted close to the point of tipping over, the non- synchronizing generator promises to yield sig-
skid material, which covers only part of the base, nificant cost savings in the production version of
lifts away from the surface and the unit slides the Picturephone set.
instead of falling on its side. All of the video cir- Beyond the quality of the picture itself, other
cuits, the camera and picture tubes, and the factors played an important part in the design of
speaker are in the display unit. The area around the display unit. For example, the camera is
the face of the picture tube has a mat black finish, placed above the picture tube to make the eye
which is ringed by a band of chrome that serves contact angle as small as possible. This is signif-
as a transition to any of the many available shell icant because, while the camera is looking at the
colors. subject, the subject is looking at the picture tube.
The picture tube face, which is 5 by 5.5 inches, The apparent "looking away" is annoying to the
displays a picture constructed in the same way viewer unless the angle is small. The least an-
as that on a home TV set. That is, it displays 30 noyance occurs when the subject appears to be
frames a second using odd-even line interlace to looking slightly down, which is frequently the
give 60 fields a second, thereby yielding an ac- case in normal conversation. Locating the camera
ceptable "flicker" rate. A complete frame con- just above the picture tube creates this effect.
sists of about 250 visible interlaced lines, and The best position for the camera has proved to
horizontal and vertical resolution are essentially be about 12 inches above the desk top so that its
equal. field of view is essentially straight ahead. Here
A near-perfect interlaced picture is provided the camera gets the most natural-looking, least
in the camera by an integrated digital synchro- distorted view of the subject, keeping him on
nizing generator, which is probably the most un- camera while allowing some movement, and (hope-
usual circuit in the station set (see Devices- fully) not picking up too many ceiling lights.
The Hardware of Progress, in this issue). The The lens in the camera has an aperture of f/2.8,
with a viewing angle of about 53 degrees. It is
normally focused for a distance of about 3 feet
The customer service unit contains the low- from the set. This distance can easily be changed,
voltage power supply, the control circuits, and the however, by moving the button above the lens to
station set equalizer, where required. The unit is the left or "20" position, changing the focal dis-
usually not in view at an office or home, and can tance to a field centered about 20 feet from the
be placed up to 85 feet away from the other units. set.
An automatic iris adjusts the lens opening for
ambient lighting conditions. The iris is of a
unique friction-free design, and is controlled by
peak averaging of the video signal. Omitted from
these measurements, however, are the upper and
lower quarters of the picture, where ceiling lights
and white shirts could unduly influence the cam-
era setting. When the iris has opened completely
(at a scene brightness of about 12 foot-lamberts)
an automatic gain control circuit in the camera
amplifier takes over control of the signal level, al-
though with increasing noise as the light level de-
creases. In good light, with a small opening of the
iris, the camera has an increased depth of field.
This effect is exactly the same as with an ordin-
ary photographic camera, where a large "f" num-
ber allows both near and far objects to be in
In addition to the camera, the display unit also
contains a loudspeaker. Since the voice coming
through the speaker is normally that of the per-
son in the picture, it is appropriate that the loud-
speaker be located as close as possible to the pic-
ture. However, since the loudness of the voice
is best controlled by the listener, the "VOLUME"
144 Bell Laboratories Record
control knob is located on the separate control
unit, which is normally at his fingertips.
The "ON" button, of course, turns the set on.
But, during a conversation, if the viewer desires
to mute his microphone, he again presses and
holds the "ON" button. This allows him to talk
to someone else in the room without being heard
by the person at the other end of the line. To re-
sume conversation over his Picturephone set, he
simply releases the button.
Although the user will normally stay reason-
ably centered on camera without giving the mat-
ter any attention, he can check his position by
pressing the "MONITOR" button on the control
unit and viewing his own picture. Pressing the
"MONITOR" button a second time returns the pic-
ture of the person at the other end of the line. If
at any time the user does not want to be seen (a
frequent concern of housewives), he (or she) can
press the "DISABLE" button and a distinctive bar
pattern will be substituted for the picture. As
with the "MONITOR" button, pressing the "DIS-
ABLE" button a second time returns the picture.
"SIZE" and "HEIGHT" controls are real contri-
butions to the versatility of the Picturephone
set. They permit the user to "zoom" his camera,
changing the field of view by more than 2 to 1 in
area, and to adjust the effective height at which
the camera is pointed. Both functions are con-
trolled from the control unit, without involving
any mechanical movement of lenses or camera as-
sembly. The adjustments are made possible by
the silicon target in the camera, because the sili-
con target doesn't "burn-in" a memory of the area
scanned by the electron beam.
The image on the camera target is always that
of a field 26 inches high by 28.6 inches wide
about 3 feet in front of the set. When the size
control is turned to its upper extreme, the entire
target is scanned, giving a "wide-angle" field of
view. When the size control is set at the lower
extreme, only a portion of the target, correspond-
ing to a field 16 inches by 17.6 inches at the 3-
foot distance, is scanned. While this narrow-
angle field is considered the normal position, res-
olution may be traded for greater field of view
either to allow the user to move around more in
front of the camera or to accommodate more
than one person on camera (see A "Solid-State"
Using the SIZE and HEIGHT controls on the con-
trol unit, a person making a Picturephone call
can adjust his (or her) own image without mov-
ing the display unit itself. The HEIGHT control
moves the image up (top, at right) or down. The
SIZE control moves the image away, in effect, or
brings it closer, electronically. A camera iris
automatically adjusts the lens aperture to com-
pensate for any differences in light intensity.
Electron Tube for the Picturephone Set, REC- heater. Top and bottom vents at the rear of the
ORD, June 1967). shell provide chimney action for cooling this heat
For any setting less than the widest angle, the sink.
user can, by adjusting the HEIGHT control, move The high-voltage power supply is encapsulated
the reduced raster to scan the top or bottom por- directly in front of the aluminum heat sink.
tions of the image. Although a mechanical tilt ad- When the shell is removed, an interlock at the
justment allows an installer to compensate for rear of the unit disables the high-voltage power
desk and chair heights, the user can later adjust supply. A strategically placed shield on the re-
the set for his own height by using the electronic ceiver reduces interference between the trans-
height control. mit and receive sections of the set. Controlling
While Picturephone service is intended pri- this interference between the high-voltage drive
marily for face-to-face conversation, visual com- pulses for the cathode-ray tube and the low signal
munication sometimes entails showing drawings, level at the camera output was the most difficult
documents, or other physical objects. This can be problem in assembling the circuits into a unit.
awkward if the customer has to hold things up in The low-voltage power supply and the control
front of the camera. Therefore, the set is de- circuits (as well as an equalizer where required)
signed so the user can point the camera down at are contained in the service unit, which uses com-
the surface on which the set rests and still keep mercial power. Since no standby battery is pro-
the picture tube in view. This is done with a mir- vided, failure of commercial power removes the
ror swivel-mounted in the display unit. It can be video portion of Picturephone service (but does
brought in front of the camera by moving the not affect the voice portion).
button above the camera lens to the "1" position. The Picturephone equipment that the Bell Sys-
The field of view of the camera when the mirror tem's customers will use has been designed with
is out is 5 inches by 5.5 inches, with the top of close attention to human factors, to simulate
the field at the edge of the ring stand. Moving as closely as possible the free and natural com-
the mirror into position also shortens the focal munication of face-to-face conversation. A mod-
distance of the lens to one foot, reverses the cam- est graphics capability is included, and adjust-
era sweep to correct for the mirror image, and ments that people will have to make are limited
locks the camera in the narrow-angle mode. The to those they are most likely to want. The Mod
resolution at this distance is adequate for simple II set is expected to serve well as Picturephone
sketches, photographs, and the like. Typed text is service becomes commercially available over the
of marginal legibility, and the 5x5.5-inch field next few years.
does not, of course, encompass an 8.5x11-inch
Inside the plastic shell of the display unit, a
heat shield at the front of the camera and a cop-
per heat sink keep the camera from getting too
hot. Both the shield and the heat sink are neces-
sary since the right place for the camera from a
human-factors standpoint turns out to be the
worst possible place from a heat standpoint. An
aluminum heat sink at the rear of the display
unit holds the power transistors for the sweep
drives and the power supply for the cathode-ray
Picturephone display units being assembled and
tested at Western Electric's Indianapolis plant.
Among the many operations: mounting the pic-
ture tube and frame assembly on the ring stand
(top left), checking circuit boards visually (top
right), placing them in the display unit (bottom
left), and finally, testing for picture alignment.
May/June 1969 147
The first customers for Picturephone set -vice will likely be business and industrial en-
terprises, where the usefulness is readily apparent. The service can be added to business
telephone systems with some changes to present PBX and key telephone equipment.
Video Service for Business
J. R. Harris and R. D. Williams
OME BUSINESS CUSTOMERS have simple, single- broad plans have been made for adding Picture-
S line telephone service much like residential
service. Others have special switching arrange-
phone service to the various types and sizes of
telephone equipment, and what development pro-
ments, either Private Branch Exchange (PBX) or jects are now underway.
centrex, and many are equipped for key telephone Initially, Picturephone service will be offered
service. (Centrex is a type of PBX service with to any customer served by selected No. 5 crossbar
additional inward and outward dialing features. switching offices. Customers will place and receive
Key telephone service means pushbuttons on tele- Picturephone calls much as they now do regular
phone sets to select additional lines and perform telephone calls. With centrex service, incoming
other functions.) Together, these arrangements video calls can be connected directly to the Pic-
provide a broad array of telephone service fea- turephone set; with either centrex or PBX ser-
tures: attendant assistance, multiple lines with vice, calls can be switched to the set by an atten-
"pickup and hold," hunting from a busy line to a dant. Picturephone display and control units can
secretary, consultation hold, conference calling, be supplied for the attendant if the customer de-
call transfer, intercom, off-premise extensions, sires, so that the attendant can see and be seen.
and many more. Another option would display a fixed video image,
PICTUREPHONE® service is a major new Bell such as the customer's trademark, to the caller
System service to be added to those now provided while the attendant is working on the call.
by the major dial PBX and centrex systems serving A new duty of the attendant will be to recognize
the business community. For the most part, the when an incoming video call is directed to a non-
current systems are step-by-step and crossbar PBX video station and to notify the calling party that
switching systems. These will supply PBX and cen- the video portion of the call cannot be completed.
trex telephone service for several years to come A question of best procedures arises when the
until electronic systems eventually displace them. caller requests that the call be completed to a
Let's look at what the business customer will voice-only telephone. Systems will permit such a
see and do in making a Picturephone call, what connection, but charging will continue as if for
May/June 1969 149
A new 850A PBX, operating in parallel with an ex- 850A PBX. Voice-only telephone calls continue to be
isting 701 or 757, will add Picturephone service switched by the regular PBX. Video and voice-only
for business customers. Both audio and video por- calls may be handled by the attendant; Picture-
tions of Picturephone calls are handled by the phone sets at the attendant's position are optional.
Picturephone service. A video call dialed directly A new video line circuit connects each Picture-
to a nonvideo line, however, will not be completed. phone line to both the 850A PBX and the regular
When a call involves more than two parties PBX. When a call is placed, the line is connected to
equipped for video, there is no immediately ob- a register in the 850A PBX and to a line finder or
vious answer to the question of who should see register in the regular PBX. Picturephone calls
whom. In general, the party who has set up the are initiated by dialing the character, #, on the
three-way connection determines who will see 12-button TOUCH-TONE® telephone, followed by
whom (see table on page 153). a normal telephone number. The # character
We expect that executives of medium and large causes the video switching system to dismiss the
businesses will be among the first customers for regular PBX and to apply a busy indication to the
Picturephone service. Most of these customers line appearance in that system. Both the audio and
are currently being served by the 701 step-by-step video signals are then handled by the 850A PBX.
or 757 crossbar systems. Other customers are Alternatively, if the called number is not pre-
served by No. 5 crossbar centrex (see Choosing ceded by the dial indicator, #, the video switching
the Route, this issue). system is dismissed and a busy indication is ap-
To add Picturephone service to the 701 and 757 plied to its line appearance. The call is then han-
PBX's, Bell Labs has designed a new Picture- dled in the usual manner by the regular PBX.
phone switching system, designated the 850A Interface between the regular telephone sys-
PBX, which operates in parallel with the existing tem and the video switching system appears at
PBX (see figure on this page). The system in- three points (see figure above). The line circuit
cludes the service features generally available interface involves only the talking pair and a su-
with other PBX and centrex systems. The PBX for pervisory lead for each line equipped for Picture-
Picturephone service uses the electronic technol- phone service. An interchange of signals is also
ogy exemplified by the 800A PBX (see Electronic required for the attendant circuitry, which is
Switching For Small PBX's, RECORD, February shared between the two systems, and for the call
1967). transfer circuits so that Picturephone calls can
1 50 Bell Laboratories Record
be transferred to a voice-only line. The video serving a growing number of customers. It is rel-
switching system is connected to the serving of- atively simple to add the video capability to PBX
fice over special six-wire trunks. and centrex services provided by No. 101 ESS. A
Two parallel four-wire ferreed switches are new four-wire wideband switch unit, which op-
used to switch the combined audio and video erates in parallel with the existing No. 101 ESS
signals for Picturephone calls. Crosspoints are switch unit, will be added to switch the video por-
mounted on new printed wiring boards designed tion of the Picturephone call (see upper figure on
to plug into carriers, which in turn are mounted page 152). It will be capable of serving 150 or
on a framework similar to the existing PBX. The more Picturephone sets. The program in the con-
new PBX will serve a maximum of 90 lines. trol unit will control this switch. The audio por-
When Picturephone service is added to a 701 tion of the call, as well as all supervisory func-
or 757 centrex system, calls dialed directly to the tions, will be handled by the regular 2A, 3A, or 4A
outside must be automatically identified (AIOD), switch unit in the normal manner. This arrange-
since no provision is being made for operator iden- ment uses the existing switch unit in handling
tification. The 850A PBX will operate with the data messages to pass control information back
MOD system available for the 701 and 757 PBX's. and forth between the control unit and the video
No. 101 electronic switching systems (ESS) are switch.
A new video switch, operating in parallel with the ready provided by No. 101 ESS. The existing data
existing 2A, 3A, or 4A switch, will add Picture- link (s) will be used for control of the video switch
phone service to the PBX and centrex services al- by the stored program in the Ess control unit.
Key telephone service will be used with PBX lines intercom lines, and regular telephone lines. When
and with central-office lines. In either case, each used with a central-office line, a Picturephone in-
key set can be served by one or more video lines, tercom provides internal video communication.
152 Bell Laboratories Record
The wideband video switch uses standard, four-
wire, 8-by-8 ferreed switches, packaged in mod-
ules which can be added to the switch unit in the
field to increase the capacity of the system. This
"add-on" type of growth encourages even distri-
bution of traffic. The video switching network and
associated control will be packaged in cabinets
compatible with existing switch unit cabinets.
Further in the future, the 810A PBX, currently
being developed, will be designed to allow Picture-
phone service to be added when desired by the
To add the video dimension to the usual types
of key telephone service and to take care of cer-
tain special situations as well, a new six-wire
video key telephone system, belonging to the 1A2
family of key systems, is being developed (see
Key Telephone Systems: The Latest Chapter,
RECORD, March 1966).
A feature of the key system (see lower illus- * These video services will be available with series 300
tration on page 152) will be a single-link inter- and centrex II service. The controlling party must be a
com accommodating up to ten Picturephone sets. PBX or centrex station (never an "outside" party).
Calls to any set on the intercom will be made Party A is the noncontrolling party first on the connection.
by dialing the character, #, plus one other digit The controlling party can add party B by flashing and
corresponding to the called station. A multi-link dialing party B's number.
intercom is under consideration.
The key telephone system will include an add-
on conference arrangement to operate with cen- With Picturephone service, the communication system must
tral office, PBX, or intercom lines. The conference play a part in control of who is seen in a three-party conference.
unit will be similar to that provided for regular
telephone service, but only one video connection
will be made at a time (see table on this page).
Video repeaters and synchronizing circuits- using key system arrangements just described. In
together with the usual lamp, holding, and audible this case the Picturephone number will usually
signaling circuits-are required in the key tele- not be the same as the PBX or centrex extension
phone system to add Picturephone service. An number. On outgoing calls the customer will se-
enlarged key service unit is planned to house lect the video line to place a call by pressing an
this equipment. This unit will accommodate two appropriate line button.
lines plus the equipment needed to switch the Pic- In the initial offering, Picturephone service is
turephone set. The switching circuitry responds not planned for off-premise extensions, tie lines,
to the pick-up key in the telephone set and per- or interoffice channels used in common control
forms the same function for video calls that the switching arrangement (CCSA) services. In the
key performs for audio calls. A four-line package, future these services and new ones may be added.
which provides four individual lines or two "boss- For example, the utility of video conferences
secretary" arrangements, will also be available. might be improved. To this end a new voice-acti-
In situations where the customer's telephone is vated conferencing system is being explored. With
served directly from the central office, he may this arrangement the speech activity of the con-
elect to use key telephone service with central- ferees controls who sees whom.
office Picturephone lines. Each key telephone set Compatibility with the Bell System's PBX, cen-
can be served by one or more video lines to the trex, and key telephone system service features,
central office, video intercom lines, and regular together with maximum use of existing switch-
telephone lines. ing capabilities and ease of installation and
When only a few people served by a PBX require growth, have been the objectives of the PBX and
Picturephone service, they can be connected di- key telephone Picturephone planning and devel-
rectly to the central office, rather than to the PBX, opment.
May/June 1969 153
As Picturephone service supplements conventional telephone service, switching arrange-
ments for video calls will be integrated with existing switching systems - initially with
No. 5 crossbar and later with No. 1 ESS - in the simplest and most direct way possible.
Choosing the Route
F. A. Korn and A. E. Ritchie
T HE DECISION to integrate PICTUREPHONE® ser-
vice with voice features leads directly to the
conclusion that the two must be combined in
Within the local office to which the customers
are connected, a separate video switching net-
work is added, parallel with the existing voice
existing local central offices. Thus, customers in network, to interconnect Picturephone calls. This
an area will most likely receive Picturephone video network is called into play only when a
service from the same office that provides con- Picturephone call is recognized. Remote switch-
ventional telephone service. These customers will ing is used wherever possible to reduce the high
be connected to the local office by the usual two- costs associated with long video loops.
wire loop for voice, which can be used independ- Achieving the desired close relationship of voice
ently, and a separate four-wire loop for the pic- and video makes it desirable to use the same tele-
ture, which can be used only with a voice loop. phone number for both services. This, in turn,
On the outgoing side of the office, the voice and requires the use of a special indicator to differ-
picture transmission facilities will be combined entiate video calls from voice-only calls. The
in a six-wire trunk and will never be used inde- choice of indicator is the twelfth button (#) of
pendently. For long-haul (or toll) connections, the TOUCH-TONE® telephone,
switching offices beyond the local level will be ar- used as a prefix, thereby tying
ranged in a hierachy similar to that now em- together Touch-Tone and Pic-
ployed for telephone traffic. Since the Picture- turephone services. The sim-
phone signal will be converted to and maintained plicity and economy of this
in digital form as it is transmitted over more signaling method easily justi-
than local distances, the toll offices will have dig- fies the tie-in, particularly in
ital switching equipment. view of the long-range plan to
At a No. 5 crossbar central office in
New York City, switchman W. R. Ack-
erson of the New York Telephone
Company and co-worker J. N. Palmer
(on screen) check operation of the Pic-
turephone system currently being tried
out by the Westinghouse Electric Cor-
poration between its offices at New
York and Pittsburgh, Pennsylvania.
P. N. Burgess and R. E. Lahr of Bell
Laboratories measure the transmission
characteristics of a wideband switch-
ing network which simulates the more
than 12 million paths available in a
No. 5 crossbar office offering Picture-
phone service. These tests were carried
out at the Columbus Laboratory in
preparation for the standard Picture-
phone service planned for the 1970's.
Any one of these false conditions could cause sonably be compensated by using fixed equalizers,
degradation of the video signal. a controlled floor plan for the wideband network
Upon completion of the FCG test, the marker i n the central office has evolved. The three-stage
applies a second continuity check to the calling video switching network is thus arranged phys-
customer video loop. Finally, before releasing ically so that variations in path lengths are held
from the call, the marker causes the outgoing to unusually precise limits: 160 feet, plus or
trunk to apply a 100-millisecond burst of a Video minus 40 feet, from the wideband distributing
Supervisory Signal (vss) on the video pair to- frame through the three link frames to the
ward the calling customer, turning his Picture- trunks, and 160 feet, plus or minus 10 feet, from
phone set on. The signal consists of the same the trunks back to the distributing frame.
series of pulses that make up the horizontal and Because the electrical distance between the
vertical sync pulses in a normal video signal but equalizers and network is relatively constant,
without the usual picture information. the design of the equalizers can be based on a
At the terminating office, similar actions oc- fixed cable loss and appropriate shaping. All
cur, but with a few differences. For example, signals coming from an equalizer to the network
only a single check of the connection is made pass through the wideband distributing frame at
since the trunk to the receiving office has already a predetermined level, making it possible to in-
been tested and only the loop to the called station terchange equalizers and network terminations
need be checked. In addition, vss is applied con- for such purposes as traffic balancing. All signals
tinuously toward the called station, starting at coming from the network to the equalizers pass
least 100 milliseconds before ringing begins. The through the distributing frame at a lower level,
combination of vss and the ringing signal causes determined by the frequency-shaping character-
the station set to give a distinctive ring, indicat- istics of the controlled cable and network.
ing a Picturephone call, and turns the set on Further steps taken to improve transmission
when the customer answers. characteristics through the office include: using
Some readers may wonder at this point whether shielded cable for all transmission pairs between
crossbar switches, originally designed to pass au- frames, separating each direction of transmis-
dio signals up to 4 kHz in bandwidth, can handle sion into two separate cables, and separating the
video signals 250 times greater in bandwidth. do control leads from the transmission pairs. A
They might also wonder whether the high-fre- network with these constraints was built and
quency noise generated by the operation and re- tested. Also, system studies were conducted to
lease of hold-and-select magnets creates intoler- give numerical limits to the transmission impair-
able interference with the video signal. These ments described earlier, and to determine how
same questions were raised early in the develop- each of the impairments could be allocated to
ment of the Picturephone system. A concerted each portion of the transmission path from Pic-
effort by system, circuit, and equipment engi- turephone set to Picturephone set. The results
neers, as well as an extensive testing program to of the testing program showed that the network
verify the designs, helped answer them. Specifi- will comfortably meet its allocation.
cally, it was necessary to learn about and reduce With the anticipated growth of Picturephone
the effects of: the transmission insertion loss of service, the No. 5 crossbar system will be ex-
the network over the 1-MHz band, the "self-cross- pected to provide new switching abilities. In the
talk" properties of the network (i.e., crosstalk i mmediate future, there is need to provide bit
between the transmit and receive pairs of the stream, or digital, switching arrangements for
same channel), the crosstalk from other video handling the interconnection of calls above the
signals, and the noise caused by relay operations local office level. Another need is for additional
in a central office. customer features such as individual call trans-
Simply using equalizers to reshape video sig- fer arrangements within a centrex group. These
nals distorted by the network would not work services are being planned now.
because the distortion of a signal would vary For the longer range future, plans are being
from call to call due to the differences in cable formulated to switch Picturephone service with
length through the various paths or channels in No. 1 ESS and to provide better concentrator fa-
the network. Since this variability cannot rea- cilities in the customer loop plant.
May/June 1969 159
The Evolution of Picturephone Service
Some recent milestones in the development of the PICTURE-
PHONE® system are summarized pictorially on these pages
(photos from The Evolution of Picturephone Service,
RECORD, October 1968).
By this time, Bell Labs scientists had developed sev-
1956 eral experimental "video telephone" systems of varying
size and appearance which offered commercial possibilities. The
one shown here was demonstrated before the Institute of Radio
Engineers on August 23. This was the first system to transmit
and receive recognizable pictures over ordinary telephone wires.
Studies and experiments continued at Bell Labs to
1957 develop an economically feasible videotelephone sys-
tem. Experiments similar to the one shown here helped engi-
neers establish such picture standards as resolution, contrast,
and other f eatures. By 1959, plans were made to develop a video-
telephone system specifically for the purpose of conducting trials.
The first public exposure of Picturephone service was
1963 A complete experimental The station setsys-
tem had been developed. in-
made at the New York World's Fair. Visitors, selected
at random, tried the service for about 10 minutes each. Results
cluded the camera-receiver-loudspeaker unit and the of interviews conducted at the conclusion of each trial provided
separate combination telephone set-video control unit. valuable information on early public reactions to the service.
Limited commercial Picturephone service be-
1964 tween public locations in three cities-New
York, Chicago, and Washington, D. C.-began on June
.25. The service was inaugurated with a call from Mrs.
Lyndon B. Johnson in Washington to Bell Laboratories
scientist Dr. Elizabeth A. Wood, at the Picturephone
center in Grand Central Terminal, New York. Robert
F. Wagner, then mayor of New York, is seated at right.
As a result of earlier trials, significant equipment and
1965 operational changes were made in the Picturephone
system. The modified equipment was used in a product trial
begun in July 1965, in cooperation with Union Carbide Corpor-
ation. In December of the same year an experimental trial be-
gan at AT&T headquarters in New York City. In June, 1967,
the trial was expanded to include three Bell Labs locations. This
trial integrated Picturephone service with normal telephone
service. This "corporate network" offered an opportunity to
explore additional uses for the system, such as the feasibility
of using the Picturephone set as an interface between man and
computer (shown here). The computer is interrogated from a
Touch-Tone® dial, and results are displayed on the screen.
The Bell System's Picturephone "see-while-
1968 you-talk" set has been redesigned to in-
corporate additional features as a result of the
extensive trials. The improved "Mod II" set shown
here is itself now the subject of further trials as
the evolution of Picturephone service continues.
Transmitting Picturephone signals across town and across the country takes advantage
of the versatility of today's nationwide communications network. Digital systems to be
introduced in the future will greatly increase transmission efficiency and versatility.
Transmission Across Town
Or Across the Country
D. W. Nast and I. Welber
Tway since the first telephonehas come awere
HE BELL SYSTEM NETWORK
long pect that customers will normally use a form of
speakerphone during a Picturephone call, the
acoustics of the customer's office or home may af-
connected over the simplest form of transmission
system-wires. Today, the transmission network fect the quality of the audio signal. Thus, control
is a complex aggregate of electronics gear and of echo and loss has been given special attention
the transmission medium (wire lines, coaxial in engineering the network.
cables, and radio paths). Together, they provide The greatest challenge, however, is the video
a multiplicity of channels over which many cus- transmission. To assure adequate picture quality,
tomers can communicate. New and more complex stringent requirements have been placed on such
services and equipment are continually being transmission characteristics as amplitude and
added to the network without disrupting or im- phase deviations, single-frequency interference,
pairing its ability to handle the many and varied random noise, crosstalk, switching noise, gain
existing communication services. The introduc- variation, low-frequency response, and power
tion of PICTUREPHONE® service is no exception. hum. As an example, for each trunk, interfering
Adding Picturephone service to the network signals from power lines must be at least 45 dB
makes it more versatile and potentially useful for below the desired signal. The requirements have
a variety of wideband communication services. been set to assure satisfactory performance on
Basically, the transmission objectives for Pic- connections involving up to six analog trunks in
turephone service are to transmit high-quality tandem.
voice and video signals and to maintain this qual- The Picturephone signals, both audio and
ity from one call to the next. One criterion in video, arrive at the local central office in analog
fulfilling this objective is to make the audio por- form over six-wire "loops"-two wires for audio
tion of a Picturephone call at least as good as and two wires for each direction of the video por-
it is in the present DDD network. Because we ex- tion. Special six-wire trunks are then used to
162 Bell Laboratories Record
carry the call outside the local area. Baseband connecting line at the far end). The toll network
analog transmission is used over exchange trunks used for Picturephone service can be administered
less than six miles in length. For longer exchange to avoid multiple encodings by appropriate engi-
trunks and toll trunks, analog transmission could neering of the switching hierarchy.
also be used, but it would not be a very practical Encoding the Picturephone signal into digital
solution, economically. Although the analog re- form at a 6.3-Mb/s rate raises the question of
quirements for long-haul Picturephone trans- optimum format. Before we can answer that
mission could be easily met by using an entire question we must know something about the
TD-2 channel, just as for television, this would
be prohibitively expensive. And it is not possible
to put together an efficient combination of analog Ralph Graham, of AT&T's Long Lines Depart-
video signals without suffering greater impair- ment, checks the operation of the digital terminal
ment than is allowable on long trunks. developed for the TD-2 microwave system. This
What is the solution? It turns out to be more terminal handles signals for the trial now in
economical for most of the longer exchange progress between Westinghouse Electric Corpo-
trunks, and for toll trunks, to transform the an- ation's offices in New York City and Pittsburgh.
alog signal to digital form, and convert it back
to analog at the distant terminal. And this is
easy to do, since digital transmission in the Bell
System is evolving rapidly. There are two very
i mportant characteristics of digital transmission
that ideally suit it for this application. First,
the digital signal can be regenerated so that the
impairments are not a function of distance. Sec-
ondly, once they are in digital form Picture-
phone, telephone, and data signals can be effi-
ciently intermixed on the same transmission
facility. By taking advantage of these charac-
teristics, line impairments-error rate and pulse
jitter-can be so controlled that their effects on
the Picturephone signals are essentially imper-
Information can be sent in a digital format
over transmission systems that use frequency-
division carrier techniques for carrying several
signals simultaneously. Sending voiceband data
over the switched DDD network is an example.
Digital information can also be sent over systems
using time-division techniques for handling sev-
eral pulse streams at one time. The T-1 system,
for example, with its pulse stream of 1.5 mega-
bits per second (Mb/s), is the Bell System's most
widely used system that is inherently digital in
its makeup. But its capacity isn't sufficient to
handle a Picturephone signal. However, the T-2
carrier system, a member in the same family to
be introduced shortly, carries a 6.3-Mb/ s signal.
The Picturephone signal can be adequately rep-
resented using this bit rate. Although a higher
bit rate would have made it easier to get the de-
sired performance, it would have been extrav-
agant from a transmission point of view.
With the decision to use the 6.3-Mb/s rate came
another one-to limit the encoding to a single
step (i.e., once the signal is in digital form it
stays in this form until it reaches the analog
May/June 1969 1 63
1 64 Bell Laboratories Record
form of the signal itself. Take the energy con-
tent of the signal, for example. Imagine a spe-
cial power measuring device that measures the
power in a narrow frequency band. If we were
to measure the energy content of the signal in
narrow steps from very low frequencies (dc) to
(Refer to (A) on previous page.) 1 MHz as a function of time and average each
Picturephone signals are encoded into digital reading over the time interval, a plot of the re-
f orm for transmission over long distances using sults would show that most of the energy is con-
a "differential PCM" system. The Picturephone tained below 50 kHz. Moreover, the curve would
signal (A) is an analog of the picture material. show that for much of the time the signal is
hardly changing at all, or if it is changing rap-
idly and introducing high frequencies, it is not
doing so very often. These properties, as we will
see later, are used in deriving an efficient digital
coding scheme for Picturephone signals.
To encode the 1-MHz video Picturephone sig-
nal into the T-2 rate of about 6 Mb/s takes two
(Refer to (B) on previous page.) basic steps: sampling and coding. Samples of the
Encoding the analog signal into a pulse stream video signal must be taken at a rate which is at
with a standard Pcm system (B) would result in least twice the highest frequency we wish to re-
an excessively grainy picture. The 1-MHz video produce. This is a fundamental law of communi-
signal is sampled at a 2-MHz rate. Three binary cation. Thus, if we wish to reproduce a picture
digits are used to code the samples. But with with resolution up to 1 MHz, we must sample
three digits only eight discrete levels can be en- the amplitude of the original signal at least at a
coded, which for purposes of this example are 2-MHz rate. Limiting the transmission rate to 6
divided equally over the maximum amplitude of Mb/ s means we are restricted to three binary
the signal. The use of only eight levels for sam- digits per sample. However, three binary digits
pling a continuous signal results in the graininess. mean that the total amplitude range of the signal
must be represented by only eight discrete levels
(see B at left).
So far we have done two things-one beneficial
and one restrictive. We have substituted a signal
that is either on or off for one that previously
had a continuous range of values-this is bene-
ficial since a two-valued signal can be reliably re-
produced with no loss in information as long as
the on pulse can be distinguished from the off
pulse. The restrictive effect is that the signal is
now represented by only eight levels, where be-
fore sampling and coding it was continuous. This
effect produces a graininess in the picture which
(Refer to (C) on previous page.) most people would find quite objectionable. To
The differential Pcm system (C) appreciably re- overcome graininess, a process called differential
duces graininess by taking advantage of the PcM is used. This process takes advantage of the
unique characteristics of the signal-i.e., most of fact that most of the energy in the signal is be-
the energy is below 50 kHz and the amplitude low 50 kHz, and the amplitude is hardly chang-
changes very little. Here a delayed signal, pro- ing at all.
duced from a PCM decoder in a feedback loop, is The encoder used for differential PCM (see C
subtracted from the original signal. Most of the at left) employs a PCM decoder in a feedback loop
eight discrete levels are arranged to represent the which produces a signal that is delayed by a
region o f the difference signal around zero; fewer small amount from the original. The delayed sig-
levels are used for larger difference signals. Al- nal, when subtracted from the original, produces
though the reproduction of a picture coded in a difference signal. When the original signal is
this way is still grainy, tests have shown that it changing slowly or not at all, the difference is
is far superior than one coded by straight PCM. zero, or nearly zero; when the signal is changing
May/June 1969 165
For the present, and until the early 1970's, TD-2 the three 6.3-Mb/ s Picturephone signals plus the
microwave radio is one, of the two means for required synchronizing and framing pulses into a
transmitting Picturephone signals over long dis- 20.2-Mbls signal. The digital terminal converts
tances. To do this, a special digital multiplex this signal into a high-speed, four-level pulse
and a digital terminal were developed to encode train. The FM terminal transforms the pulse
up to three Picturephone signals on one TD-2 train into a frequency-modulated wave, which is
radio channel. The digital multiplex combines sent to the TD-2 microwave radio transmitter.
A special digital multiplex and terminal is being eight-level pulses instead of the four levels used
developed to permit the L-4 coaxial cable system in the TD-2. Two digital Picturephone signals,
to carry digital Picturephone signals over long applied to the L-4 system, can occupy the fre-
distances. The signal produced by the terminal quency band normally used .for any of the L-4
used with the L-4 system is a pulse stream with mastergroups except the bottom mastergroup.
166 Bell Laboratories Record
rapidly, the difference is large. At this point we produced by the digital terminal being developed
take advantage of the fact mentioned earlier that for the L-4 system is a pulse stream with eight-
most of the time the signal is changing slowly, level pulses instead of the four levels used in the
and thus, most of the time the difference signal TD-2. In addition, a special signal format, known
would be near zero. This being the case, we can as "partial response" filtering, takes advantage of
arrange the eight coding levels so that most of the properties of the coaxial cable. This format
them are used to represent the region around produces a spectrum with essentially no energy
zero. Fewer levels are used for the larger differ- at the band edges of the mastergroup. (A master-
ence signals. The reproduction of a picture coded group is a composite signal which carries up to
i n this way is still subject to some graininess when 600 voice channels.) This is done to minimize in-
the signal is changing rapidly, such as a rapid terference into adjacent channels and to permit
change from black to white or vice versa. How- timing and synchronizing signals (pilots) to be
ever, the results of subjective tests performed placed at the band edges.
with a coder of this type are far superior than Two digital Picturephone signals, applied to
for a straight Pcm coder. the L-4 system, occupy the frequency band nor-
The digital transmission system that will carry mally used to carry a single mastergroup. The
the signals between distant points can assume a L-4 system can carry six mastergroups. Any or all
variety of forms. For the present, and until the of the mastergroups may transmit encoded Pic-
early 1970's, TD-2 microwave radio and the L-4 turephone signals, with the exception of the
coaxial cable system will handle most Picture- bottom mastergroup. The distortion introduced
phone signals. The T-2 digital carrier system, by the repeaters in the band set aside for the
first of the toll digital systems scheduled for in- bottom mastergroup is more severe than in the
troduction in the early 1970's, will carry Picture- other mastergroups, and the performance for
phone signals, where appropriate, over interex- digital transmission is, therefore, inadequate.
change trunks for distances up to several hun- When only a few toll trunks are needed, TD-2
dred miles. Still further in the future, the L-5 and L-4 systems will take care of these Picture-
and T-5 coaxial cable systems and eventually phone requirements quite handily. But later
millimeter waveguide will be available for long- when many such trunks are needed along a major
haul transmission of Picturephone calls. route, new digital 'systems will provide the most
Since the TD-2 and L-4 systems are designed economical answer. It works out this way: For
around frequency-division carrier techniques, message channels, the analog systems using ra-
they require special terminals to permit digital dio and coaxial cable are very efficient, and even
signals to be transmitted efficiently. The special T-5, a family of digital systems for possible use
digital terminal developed for the TD-2 (see on coaxial cable in about 1975, will probably be
upper figure on facing page) will enable up to a slightly costlier way of getting voice circuits
three encoded Picturephone signals plus the re- than will its analog cousin, the L-5 coaxial cable
quired synchronizing and framing pulses to be system. But the digital systems will have a
carried on one radio channel. The bit rate on the marked advantage when it comes to handling
radio channel will be 20.2 Mb/ s. The format of Picturephone signals because of the tradeoffs
the signal applied to the TD-2 channel consists involved. For example, a TD-2 radio channel can
of the 20.2-Mb/s digital pulse train with each carry 1200 message channels but only three Pic-
pulse having four possible levels. A single pulse, turephone channels-a tradeoff of one Picture-
therefore, carries two information bits, and the phone channel for 400 message channels. Sim-
pulse rate on the channel is 10.1 million pulses ilarly, the L-4 system substitutes two Picture-
per second. Evaluation of the performance of this phone channels for 600 message channels, or one
system shows it to be highly satisfactory. Even Picturephone channel per 300 message channels.
when the radio channel undergoes selective fad- In contrast, the T-2 carrier system, designed es-
ing and is about to switch to the protection chan- pecially for digital transmission, will displace
nel, the maximum error rate in the digital signal only 96 message circuits to carry one Picture-
is less than one in 100K. This produces a barely phone channel. And future digital systems, such
perceptible amount of noise in a Picturephone as the T-5 system, will have a corresponding ad-
signal. vantage over future analog systems in efficiency
The L-4 coaxial cable system (see lower figure for transmitting Picturephone signals.
on facing page) is not subject to fading or large The discussion thus far has covered the method
variations of noise level, and accordingly, the for- used to transmit the Picturephone signal over
mat of the digital signal is different. The signal long distances. We must also transmit the signal
May/June 1969 167
over shorter distances (about six miles or less) change enough to give excessive distortion. In
between central offices. Transmission of Picture- fact, a 5-degree change in cable temperature
phone signals over this distance is in analog without a corresponding change in the equalizer
form over interoffice exchange trunks. The ex- setting will cause appreciable distortion. To com-
change cables can be as large as 1100 pairs of pensate for this, a temperature regulating equal-
22-gauge wire in one sheath and are presently izer responds to changes in the level of a 1-MHz
used for two-way transmission of 4-kHz telephone tone, applied to the trunk continuously.
channels. Trunk facilities are made up of six The previous discussion assumes that the vari-
6000-foot sections in tandem, and as many as ous pairs in a cable have the same loss versus
four trunk facilities may be built up to complete frequency characteristic and the same temper-
a connection between central office switches. ature coefficients. This is not the case, and for
Transmission of a 1-MHz video signal over this this reason a "mop-up" equalizer, operating on
medium with minimum degradation of the sig- the same 1-MHz signal used by the line equalizer,
nal requires precise equalization. Thus, equalizers will be provided at the receiving office of each
will be placed every 6000 feet, with power sup- trunk. The 1-MHz tone is supplied continuously
plied over the same line. by each outgoing office equalizer. An additional
The equalizer contains several networks that 100-kHz tone, used at the incoming office to pro-
compensate for the distortion introduced by vari- vide a second reference point for mop-up equal-
ation of attenuation with frequency in the cable. ization and temperature regulation, is also sup-
Equalizers are designed to have the equivalent plied by the outgoing office equalizer, but only
attenuation of cable lengths of 3000, 1500, and when the Picturephone signal is not present.
750 feet, thus restoring all frequencies to their It seems certain that future work on trans-
original intensity. One network, which matches mission systems to carry Picturephone signals
the characteristics of a 750-foot length, is vari- will be concentrated on increasing transmission
able to accommodate variations in the length of efficiency. The introduction of new digital trans-
trunks, or variations in characteristics that can mission systems in the 1970's will be a major
be equalized by an equivalent change in length. A step toward meeting this objective. In the mean-
temperature-regulation section is also included to time, our ability to send high-speed digital in-
avoid seasonal adjustments of the equalizers. The formation over existing analog systems is a prac-
normal variation of cable temperature over the tical beginning for a digital network that can
period of a year can cause the transmission to reach virtually every part of the country.
1 68 Bell Laboratories Record
Telephones are connected to central offices over a vast network of aerial and under-
ground wires called the customer loop plant. This network will soon carry video as well
as voice calls, as the new Picturephone service evolves and becomes more widely used.
Connecting the Customer
F. T. Andrews, Jr., and H. Z. Hardaway
I offered1970'x, as many special services willof-
N THE PICTUREPHONE®
by the Bell System over existing cus-
loop for two-way Picturephone service. The ex-
isting loops are designed for transmission of
tomer loops, just are voice signals, which are in the 4-kHz frequency
fered today. These wire networks, built up over range. But the video frequency band is much
the years primarily for economical voice com- wider-about 1 MHz-so that transmission losses
munications, will soon take on the more stringent are much greater, and some form of signal re-
requirements of video transmission. While some constitution is needed. This is where equalizers
changes will obviously be required, the loops will come in.
remain basically.the same. Picturephone service Adding equalizers is the most significant
will be incorporated by modifying existing loops, change required to adapt existing loops for Pic-
not by replacing them. turephone service. The equalizer is a basic re-
Adapting customer loops to accommodate Pic- quirement of Picturephone loops, providing gain
turephone service depends upon a number of equal and opposite to the loss of ordinary tele-
factors, including distance of customer from the phone cable pairs within tenths of a decibel
office, age of wire facilities already there, prox- across a frequency band from 1 Hz to 1 MHz.
imity of interference sources, type of plant con- Determining how many equalizers should be
struction (aerial or underground), and the area added, and where, is essential to make best use
being served (urban, suburban, or rural). of existing plant.
The existing loop plant consists of conventional For example, there are practical limits to how
wire pairs, each telephone line requiring one long a section of cable can be handled by an
pair. For two-way video transmission, two addi- equalizer at a given location. While separate pairs
tional wire pairs must be used, forming a six-wire are used for transmitting video signals to and
May/Tune 1969 169
Should the combined gain of the equalizers ex-
ceed the combined loss of the crosstalk paths at
any frequency in the band, high-level oscillations
will result. This is, of course, most likely to hap-
pen at the higher frequencies, where the equal-
izer gain must be high and crosstalk loss is low.
Transmitting two directions in separate units
within the same cable helps, but is not always
practical. Thus, maximum equalizer spacings
have been established for the wire gauges being
used in Picturephone loops (see table on page
172), limiting the gains to values unlikely to
cause high-level oscillation.
Actually, two different versions of the equal-
izer are required to satisfy the transmission re-
quirements of Picturephone service (see illus-
stration on page 172). One version is adjustable
The need for equalizers in a cable carrying 1- to match the characteristics of sections of cable;
MHz video signals is evident in this example of the other has fixed gain and frequency character-
the loss of two lengths of 22-gauge pulp-insulated istics to match runs of wire within central of-
cable. For a given gauge, plastic-insulated con- fices. Build-out networks and test access points
ductor cable has somewhat less transmission loss. (not shown in the illustration) are necessary to
align the system. The equalizers located in man-
holes are powered in series over the same pairs
used for signal transmission.
The equalizers cannot be adjusted to match the
cable characteristics perfectly, nor do they track
the changes in those characteristics caused by
temperature variations. Each equalizer section
contributes some residual distortion which, if al-
lowed to accumulate, would be manifested as
"echoes" or ghost images at the Picturephone
set. The resulting deterioration of the picture de-
pends directly on the intensity of the ghost im-
ages and the extent of their separation from the
main image. As a way of measuring this kind of
problem, signal distortion is translated into what
is called an "echo rating," which is an overall
When equalizers for both directions of transmis- evaluation of the transmission characteristics of
sion are installed at the same physical location, a loop with equalizers added for video service.
there is some possibility that the output of one To determine whether existing customer loops
can feed into the input of the other via crosstalk are suitable for high-frequency signal transmis-
paths (arrows) and cause "singing." This is pre- sion, the performance of these loops with equal-
vented by keeping the combined gain of the equal- izers added is simulated on a computer. The sim-
izers from exceeding the combined loss of the ulation program decides where equalizers are
crosstalk paths, using shorter equalizer spacing. needed and simulates the adjustment they would
receive in the field. The resulting echo rating in-
dicates whether the particular loop configuration
from the customer (in addition to a single pair is suitable for system use.
used for transmitting voice signals in both di- Picturephone service will first be offered in ur-
rections), for practical reasons equalizers for the ban areas. Tests of selected loops in New York
two directions are installed at the same physical City and Pittsburgh have confirmed that existing
locations along a cable run. As a result, the out- facilities in those cities can be used for Picture-
put of one feeds into the input of the other phone service, as it is now planned. (A product
through the undesired but inevitable near-end trial between these two cities is now being run,
crosstalk paths (see illustration on this page). in cooperation with the Westinghouse Electric
170 Bell Laboratories Record
T. A. Sickman of Bell Laboratories tests and adjusts equalizers
to be used in Picturephone loops. The equalizers are connected
to a 6000-foot length of test cable to simulate a customer loop
arrangement. In addition to providing gain compensation,
equalizers are used to correct distortion of the video signal.
The video portion of a Picturephone loop is added Equalizers in manholes are powered in series over
in parallel to the existing telephone loop network. the same wire pairs used for signal transmission.
Corporation.) As the service is extended toward tial urban Picturephone service. But, as the
suburban areas, many additional factors will service expands, all the various transmission ir-
have to be considered. regularities at video frequencies will have to be
Customer loops for ordinary telephone service, checked carefully.
for example, are designed to resistance limits Additionally, it has always been difficult to pre-
which insure satisfactory dialing and talking re- dict the growth pattern of the lines and services
gardless of the distance between the office and for a central office area, and to predict needs
the customer. This is accomplished by using a along any given cable route. These uncertainties,
range of wire gauges (19, 22, 24, and 26 gauge) and the fact that it is difficult to get at indi-
and adding inductances, called loading coils, at vidual wire pairs in pulp-insulated distribution
6000-foot intervals on loops longer than 18,000 cable, have led many telephone companies to in-
feet. It is common to find a combination of wire stall cables with "bridged taps." That is, several
gauges and both paper pulp and plastic-insulated "taps" are connected to the individual wire pairs
conductors in a single customer loop. Such an at intervals along the cable as it is installed.
arrangement appears to be satisfactory for ini- Eventually one tap on a pair is used to connect
a customer's telephone service; the unused con-
nections are called bridged taps. Loops containing
bridged taps more than 100 feet long cannot be
equalized adequately for Picturephone service.
Survey results show that the overall Bell System
average bridged tap per main station is 2500 feet
long. Thus, removing bridged taps will be a nor-
mal step in preparing loops for video transmis-
Further growth in dedicated outside plant (see
Access and Control Points for Dedicated Outside
Plant, RECORD, February 1967) and unigauge
(see Unigauge-A New Subscriber Loop System,
RECORD, September 1967) will eventually result
i n a plant more uniform and easier to adapt for
high-frequency services. In the dedicated plant
concept, pairs without long bridged taps are
The maximum cable lengths shown take into ac- permanently assigned to existing and probable fu-
count variations in cables and underground tem- ture customer locations. The unigauge concept
perature. They will be used as guides for install- makes it possible to serve customers up to almost
ing equalizers in loops for Picturephone service 6 miles away from a single central office, using
except where special circumstances, such as high only 26-gauge wire and range extenders from cen-
impulse noise levels, necessitate closer spacing. tral office to customer. These and other concepts
172 Bell Laboratories Record
will be incorporated as Picturephone service
grows, thus helping to assure the successful
blending of old and new services and facilities.
Another consideration in designing equalizers
for customer loops is the variation in transmis-
sion losses resulting from temperature changes
in the cable. The temperature range for buried
plant about 18 inches down is about 32 to 75 de-
grees F. Temperature variations of aerial plant,
on the other hand, track the surrounding air
temperature, and increase about 20 degrees more
when there is direct warming by the sun. Today,
the trend is toward placing all new plant under-
ground wherever possible. By 1975, practically
all new residential distribution cable installed by
the Bell System will be out of sight. This trend
will help reduce both seasonal and day-to-day tem-
perature changes in the loop plant, and thus pro-
mote more stable electrical performance.
As Picturephone service spreads into the sub-
urban and rural areas, there may be a problem
with radio-frequency interference, since much of
the loop plant in these areas includes aerial cable.
Unshielded aerial drop wires act as antennas for
radio waves impinging upon them, and the 1-MHz
range of the video signal overlaps the 0.5-to-1.6-
MHz range of powerful commercial broadcast
transmitters. Shielded drop wires and access
terminals, short equalizer spacing, and low-pass
filters can all be used to combat interference. The
specific approaches used will depend on each par-
ticular situation. Studies are under way to im-
prove our understanding of the interference to
be expected in the frequency range of Picture-
Like all significant changes in the customer
loop plant, the introduction of Picturephone
service will require revisions to current plan-
ning, engineering, installation, and maintenance
methods. Techniques of dealing with interference
and the other problems will evolve as they have
in the past. The administration of Picturephone
loops also will be more involved. Since these loops
contain equalizers, they cannot be rearranged as
simply as conventional telephone pairs, but will
have to be segregated in much the same way that
special service loops are today.
Further in the future, improved new cable de- M. F. Veverka and E. W. Banz, Jr., both of Bell Laboratories.
signs, which have been under development for measure electric field strength and the associated interfer-
voice use, will also help us do a better job of ence on telephone lines to help determine the need to prevent
meeting the combined needs of voice and video radio frequency interference with the 1-MHz video signal.
transmission. Just as the present ways of engi-
neering and constructing loops have grown out
of successive improvements, so too will the Pic-
turephone loop network evolve as we learn and
progress from each successive experience.
May/June 1969 173
The Picturephone system is possible in an economical form because of recent develop-
ments in electronic components technology. How recent is best illustrated by the inte-
grated circuit devices in the display unit, as well as by its picture and camera tubes.
The Hardware of Progress
S. O. Ekstrand
NYONE SCANNING a list of the electronic de- For example, the tube's deflection yoke is posi-
A vices used in the PICTUREPHONE® system will
gain insight into the meaning of technological
tioned during manufacture and then permanently
fastened in a polyurethane encapsulation. In ad-
evolution. On this list are devices that would dition, frame-centering projections are molded
have been impossible to produce only a few years i nto the encapsulation so that the tube can be eas-
ago-devices, for example, that draw heavily on ily centered in its enclosure. These and other fea-
recent silicon and thin-film technology. This ar- tures make installation a relatively simple job
ticle will limit itself to describing eight devices -and a safe one, since the rock-hard polyure-
that most clearly embody the latest advances in thane also serves as a protective shield. A fur-
the technology of electronic components: the pic- ther margin of safety is supplied by a glass panel
ture tube, the camera tube, and six integrated- that is bonded to the face of the tube. This panel
circuit devices. All eight were expressly designed serves a double purpose: Its surface is lightly
for the Picturephone display unit. etched to reduce glare in brightly lighted rooms.
The picture tube is an electrostatically focused Like all telephone devices, the display tube had
cathode-ray tube with magnetic deflection. Of the to be designed for long life. Its envelope is made
eight devices, it is the only one the customer will of a special glass that is highly resistant to the
see and, inevitably, it will remind him of his discoloration caused by electron bombardment,
home television set. However, there are signif- and all of its electrodes are designed to meet ex-
icant differences-most of which add up to greater acting electrical tolerances. A case in point is the
safety, reliability, and economy of installation. cutoff voltage required for grid number one.
May/June 1969 1 75
This voltage is the minimum needed to stop the performance adversely is the target's "dark cur-
electron-beam flow entirely. In the drive circuit rent"-that is, the leakage current generated by
of an average cathode ray tube, the cutoff voltage the diodes even in total darkness. Excessive dark
would have to have an allowable range of 30 volts current limits the maximum contrast of the pic-
or more. In the Picturephone set, however, the ture. The problem is created by two kinds of dark
cutoff voltage needs a range of only 15 volts, current, known as "surface generated" and "bulk
which permits more economical circuitry. What generated." The surface-generated dark current
makes this reduced range possible is precise con- is due to surface-state energy levels that exist at
trol of spacings and grid aperture sizes during the silicon dioxide interface. Although these en-
manufacture. ergy levels arise from a number of different
In life tests, the tubes have been living up to causes, they can be collectively measured and con-
their design objectives and continue to deliver sidered as a single phenomenon. At one time, the
high and constant output. They show negligible surface-state energy levels were a major source
loss in brightness after eight to ten thousand of dark current, but improved processing of the
hours of continuous operation, and there have silicon target has virtually eliminated this prob-
been no indications of discolored glass. lem. Similarly, bulk-generated dark currents-
The camera tube is even more a product of which are due to the activity of charge carriers
modern technology than the picture tube. (See within the bulk of the silicon-are now held to a
A "Solid-State" Electron Tube for the PICTURE- minimum by proper processing of the silicon.
PHONE Set, RECORD, June 1967). This unusual The structure of the electron gun also plays a
tube uses a target consisting of an array of more part in holding down dark current: The gun's
than half a million silicon diodes in an area ap- elements are arranged so that all light from the
proximately one-half inch on a side. The diodes cathode and heater is barred from the target, and
are reverse biased and scanned by an electron dark current due to this light is minimized.
beam. A thin resistive film over the target's face Mechanical strength and alignment of the
prevents the beam from charging the silicon di- newer tubes have also been much improved. The
oxide surface to the point where it would reflect gun's electrodes and ceramic spacers are brazed
the beam. together by a pass through a furnace. And to en-
One of the things that can affect the tube's sure accurate alignment of the beam-stripping
electrode (which trims the beam's diameter to
0.003 inch), laser technology is called upon: The
electron-gun structure is completely assembled
and then a pulsed ruby laser is used to drill a
0.003-inch hole through the beam-
stripping electrode. The resulting
Cutaway view of the Picturephone set's camera alignment is precise enough to guar-
tube (top). The silicon target is immediately be- antee maximum beam transmission.
hind the lens at the right. Thin enough to be The mounting of the silicon target
translucent, the target has over half a million has a minimum number of parts, so
silicon diodes in an area about the size of a that manufacture is simplified and ca-
nickel. Like the display tube, the camera tube pacitive coupling between the target and
uses electrostatic focusing and magnetic deflec- other elements is mini-
tion. The entire tube is shielded by high-permea- mized. In addition, the ex-
bility magnetic material. The insert below the ternal terminal of the
camera tube shows the "mesh" electrode, which "mesh" electrode (which.
f orms a uniform field between itself and the target. forms a uniform field be-
tween itself and the target)
has been placed close enough
to the target area to allow
(Bottom) The display tube is essentially a "plug- a common ground reference for both the
in" device and requires no adjustments during mesh and the target. This arrangement
installation. The deflection yoke is positioned eliminates ground loops between these ele-
during manufacture and permanently set in place ments and minimizes noise from induced
when the tube is encased in polyurethane plastic currents.
(shaded area). Projections molded into the plastic The camera tube is supplied ready for
make it easy to center the tube in the display set. use and comes with its magnetic deflection
coils prepositioned. The electron beam is mag- 16 circuits include a complete four-stage binary
netically aligned within the gun during manu- counter and use 72 transistors and 111 resistors
facture, and the tube is enclosed in a high-perme- to form 40 logic gates. These gates are designed
ability magnetic shield. All of this eliminates the to assure reliable low-power operation even with
need for any adjustments after manufacture, considerable variation in component parameters.
which means that the tube is essentially a plug-in Their high tolerance for variation makes possible
device. high manufacturing yields-another contribution
The six integrated circuit devices that control to economy.
the camera tube are the products of the same up- The count-by-16 circuits are used to divide the
to-date technologies. The devices are: a voltage sync clock oscillator's basic frequency of 16.26
regulator, a linear video gate, a video gate logic kHz to get a vertical sweep frequency of 60 Hz
circuit, a synchronizing clock oscillator, a syn- and ensure precise field interlacing. A similar,
chronizing tip generator, and a synchronizing "miscellaneous logic" chip supplies 46 logic gates
clock logic system. of the kind used in the count-by-16 circuits.
The voltage regulator maintains a critical sup- Made up of 74 transistors and 116 resistors, the
ply voltage for the sync clock oscillator and the chip handles all the gating for the timing func-
horizontal and vertical sweep generators for the tions that control the camera tube. This circuit
camera tube. It is designed to supply 12 volts has the most logic gates per chip and the highest
( ± one percent) with a load carying from -10 packing density of any integrated circuit pres-
to -30 milliamperes do and line voltage varying ently being supplied by the Western Electric
from 16 to 24 volts do over a temperature range Company.
of 0 to 60 degrees C. Physically, the regulator The complete video gate is made up of two sili-
consists of three silicon chips-a junction field- con monolithic integrated circuits. One, a linear
effect transistor, a voltage reference diode, and video gate, is a single-pole, double-throw switch
a silicon monolithic integrated circuit. All three for coupling the desired video signal through to
are mounted in an eight-lead transistor type en- the output with negligible loss, while providing
capsulation that has adequate power dissipation almost total isolation from undesired signals. It
capabilities. is used to achieve the MONITOR feature as well as
The sync clock system supplies all of the tim- some other features. The second of the two mono-
i ng signals for the Picturephone set's camera. lithic circuits is a video-gate logic circuit that
These signals control the horizontal and vertical drives the appropriate indicator lamp on the con-
sweeps, camera blanking, gating for the auto- trol unit and also supplies do control signals for
matic gain control and video clamping, and the the linear video gate circuit.
formation of the sync output signal. The precise To produce these devices in a reasonable
time constants needed to maintain precision are amount of time without sacrificing reliability or
achieved with thin-film capacitors and resistors. economy, Bell Labs device designers had to work
Amplification and buffering functions are handled very closely with designers of the Picturephone
by a separate silicon monolithic integrated cir- set and with the Western Electric Company engi-
cuit chip. A similar combination of thin-film and neers who will eventually be responsible for man-
silicon integrated circuits is used ufacturing them. To smooth the transition from
for the sync tip generator. This design to manufacture, a joint development and
circuit provides an accurately manufacturing facility was installed-at the Bell
timed pulse that is combined Laboratories location at the Western Electric
in the sync clock logic cir- Plant in Reading, Pennsylvania. Planned by a
cuitry to form the sync out- team of engineers from Bell Labs and Western
put signal. Electric, this installation has facilities for de-
Two "count-by-16" cir- veloping all the devices described in this article.
cuit chips plus a "mis- All planning was done with an eye toward early
cellaneous logic" chip pilot manufacture.
supply the necessary The fabrication area is a series of clean rooms
logic for converting the specifically designed to satisfy the stringent re-
output of the sync clock quirements of semiconductor and electron tube
oscillator and the sync manufacture. The area is supplied with filtered
tip generator into the and air-conditioned air, which is monitored to
required six timing ensure a dust count no greater than 500 particles
signals. The count-by- per cubic foot. The flow is pseudolaminar, with
Bell Laboratories Record
air entering through the ceiling and exhausting
through specially constructed walls. Laminar-flow
clean hoods are installed at work stations where
the most critical operations are performed. The
dust count at these stations is never more than
10 particles per cubic foot in normal use.
The installation also has separate vestibules in
which shoes are machine brushed and special
clothes donned. Particular attention was given to
the construction of the ceiling and floors so as to
permit easy maintenance. To ensure special clean-
liness in critical areas such as the photo-resist
rooms, these rooms are held at a higher pressure
than others. Services such as gas and water also
receive special treatment: Before entering the
rooms, the gases are filtered and dried, and the
water (deionized) is double filtered.
In addition to technical people from Western
Glenn Hill of the Western Electric Company makes final mi- Electric and Bell Labs, the installation has many
crometer adjustments of an encapsulation mold for the Picture- Western Electric operating personnel. Their pres-
phone display tube. The adjustments accurately position the ence affords them early exposure to the new tech-
tube before polyurethane is poured in. Centering projections nologies, which is important, since they will later
molded into the polyurethane facilitate installation of the tube. serve as the nucleus of the manufacturing force.
The advantages of this arrangement are two-
fold: The Western people have a chance to pre-
pare for manufacture at an early stage, and the
Bell Labs people have a chance to benefit from
their advice. The result is that many of the de-
velopment tools, fixtures, and machines can be
easily incorporated into future manufacturing
A pulsed ruby laser inside this "black box" en-
sures precise alignment of the camera tube's
beam-stripper-the electrode that trims the elec-
tron beam to a diameter of 0.003 inch. After the
beam stripper is aligned with other electrodes,
the laser bores a 0.003-inch hole through it. Bob
Sell, on assignment to the Reading Laboratory
from the Western Electric Company, is shown
loading an electron-gun structure into the unit.
He will use the television monitor to aim the beam.
Planning maintenance procedures for Picturephone service requires a considerable de-
gree of foresight. Practices suitable for only a few customers initially will still have to
be viable in the future when video service is as widespread as telephone service is today.
Keeping the System in Trim
A. E. Spencer
ODAY, as PICTUREPHONE® service makes its arrangements for new equipment is to consider
T first appearance, we are relatively unencum-
bered with previous maintenance procedures. This
present practice. Maintaining the telephone plant
today is a complex job that requires the efforts
gives us a unique opportunity to plan overall of a large number of the Bell System's employ-
maintenance arrangements before the service is ees. Their efforts are directed at detecting, locat-
introduced-although, obviously, new arrange- ing, and repairing troubles in three general
ments should fit in with existing ones as much as areas: (1) loops and customer equipment, includ-
possible. ing PBX's, (2) interoffice trunks, and (3) switch-
With this freedom, however, comes the challenge ing offices. For performing these tasks, mainte-
to plan ahead so that maintenance arrangements nance personnel have a variety of test equipment
initially required for only a relatively few custom- at their disposal, ranging from simple meters to
ers in one or two cities will still be valid or adapt- highly sophisticated equipment capable of mak-
able when Picturephone service is as widely ing many complex tests automatically.
used as the telephone is today. This article de- Yet, in spite of all this test equipment, our
scribes how the Bell system is preparing to meet ability to detect and locate troubles is not always
the challenge. Of necessity, our present emphasis satisfactory. All too often, we are not aware of
is on planning rather than on accomplishment. trouble until the customer reports it. And all too
Much of the circuit and equipment design is still often, a repairman must be sent into the field to
in progress, and it is impossible to work out all locate that trouble. He, in turn, may have to work
the details of a maintenance plan until the de- with another man in the central office-all of
tailed nature of equipment and circuitry is known which is time-consuming and expensive.
and some operating experience is gained. In planning maintenance for the Picturephone
The starting point for planning maintenance system, we have tried to improve our ability to
Plans for station and loop testing include a sta- test center (to the right, below) that will be able
tion test line that will permit convenient testing to perform a number of tests on all equalizers be-
of newly installed Picturephone sets and a local tween Picturephone sets and the central office.
detect, locate, and repair troubles while keeping Picturephone service is expected to be signif-
overall costs down. Similarly, we have tried to icantly better than present telephone maintenance.
i ntegrate maintenance for the Picturephone sys- The tester can cause signals to be looped back at
tem with existing telephone maintenance prac- the Picturephone set and at all intermediate
tices. For the voice channels of the Picturephone equalizers in the loop. Both ac and do tests can be
system (see the diagram at top of this page), the made of the equalizers. Since the equalizers are
station and loop testing arrangements are iden- powered over the loop and draw relatively fixed
tical to those being used today for conventional currents, simple voltage and current measure-
telephone service. For the video channels, the ar- ments can be made to locate open or short cir-
rangements are similar but are considerably im- cuits on the line within an equalizer section.
proved in that tests made at maintenance centers It will also be possible to send a low-frequency
and local test desks are expected to be much more signal out over the video portion of the loop to
effective in locating troubles. control an equalizer in such a way that the signal
In new installations, an installer will be able will be returned from it if the equalizer is work-
to make a number of simple but valuable tests ing. It will then be possible to loop similar sig-
with a "test line" (shown to the right of the nals back through the second and third equal-
video switch in the block diagram). After com- izers, if there are any. This procedure should
pleting an installation, he can dial the video pre- make it possible to locate faulty equalizers before
fix (#), followed by a three-digit test access dispatching a repairman.
code and the last four digits of the line he has Following successful completion of these simple
installed. The central office will then connect the tests, it will be possible to transmit a video test
new line to the test line, and the installer will pattern to the video set. If the set is on hook, the
hear a tone.' Now, if he flashes his switchhook video signal will be returned to the test position
and hangs up, the central office will transmit the through the loop-back feature at the station.
special Picturephone ringing signal to test this Measurements of received signal level, quality,
aspect of the new set's operation. When the in- and other factors will then permit further trouble
staller answers, he will be able to make a number analysis.
of other tests, including some relatively simple The arrangements for interoffice trunks are
video tests. different. (See the diagram on page 185.) Since
If the tests show that performance is not sat- the initial number of interoffice Picturephone
isfactory, or if trouble develops later, it may be trunks will probably be quite low, the trunk test
necessary to test the line from the new wideband facilities will be manual at first, and not auto-
local test desk. Here is where maintenance for matic. For very small offices, all trunk mainte-
182 Bell Laboratories Record
nance may be done with maintenance center fa-
cilities, and no wideband trunk test position
should be required. As service grows, however, a
wideband trunk test position may be installed,
and, ultimately, automatic test facilities for video
trunks will probably be developed to complement
those now being designed for audio trunks. The
test facilities will have appropriate access to
the central office switching network so that all
parts of tandem and intertoll trunks may be
In general, the tests that can be made on trunks
that carry analog signals will be similar to the
tests that can be made on loops. Although the de-
tails of equalizer designs will be different, there
will be similar facilities for locating troubles
within any section between two equalizers.
In No. 5 crossbar, conventional jack access to
all audio trunk pairs will be provided for testing.
Besides allowing a testman to make normal trans-
mission tests, these jacks will give him direct ac-
cess to signaling leads as well as a way of making
the facility busy simply by inserting a suitable
plug. Insertion of the plug will also make the
corresponding video facility busy. With ESS, the
more convenient switched access, rather than
jack access, will be provided to test both audio
and video trunks.
Today, we have a series of test trunk termi-
nations in distant offices that can be reached on
a dial-up basis for conventional audio trunk test-
ing. For Picturephone service, we will have an
equivalent series for video trunk testing. For ex-
ample, one type of test trunk will terminate the
receive direction of the video facility in a match-
ing impedance and will generate a short burst
of 1-kHz tone over the transmit direction as well
as over the audio channel. After this, the trans-
mit direction of both the video and audio facil-
ities will again be terminated in a matching im-
Another type of test trunk will have facilities
for Picturephone service and two-man testing
between test-boards using a wide variety of test
equipment. A third type of trunk will terminate
The new wideband trunk test positions now be-
ing planned for the Picturephone system may look
like this artist's rendering. Located at central
offices, the trunk-test positions will be equipped
with several test instruments new to telephone
maintenance. Among these are wideband oscillo-
scopes for analyzing video signals and "echo-
rating" test sets for measuring echo in trunks.
the receive direction and supply a steady source of 1-kHz tone over both the video and audio facilities in the transmit
direction. After about 20 seconds, the test tone will be removed, and the receive side of the trunk will be connected to
the transmit side. Still another type of trunk will permit signaling tests by cycling, the trunk through on-hook and off-
A major difference between trunk and loop testing is that trunk testing arrangements will have to include tests of digital
facilities, whereas loop testing arrangements will not. Codecs (devices for coding and decoding video signals in digital
form) will be used only with trunks, and provisions will have to be made for testing them. In general, the basic test of a
codec will involve a loop-back in which a test signal is first coded in the coder and then connected back to the decoder.
At the decoder, the test signal will be decoded for comparison with the input signal. For such testing, the codec will
most likely be controlled over a direct path from the maintenance center and the wideband trunk test position-at least,
initially. As the use of digital facilities increases, this procedure will probably change.
Maintenance of the switching equipment itself will generally follow procedures already in use. For example, in the case
of No. 5 crossbar, trouble record indications will be received from alarms and trouble cards just as they are today. In
the case of No. 1 ESS, of course, the maintenance control console and maintenance teletypewriter will be the focus of a
testman's activities. In both cases, he will follow normal routines to locate and repair the trouble.
As a trouble detection technique, not only in switching equipment but in transmission facilities as well,an ac continuity
test of the video path will- be made prior to every call. This test will not only help in the detection and location of
troubles; but will also improve the level of service received by customers. Implementing the overall maintenance plans
Artist's rendering of what a local test desk for the Picturephone
system might look like. Such "desks will be installed in centralized
locations to test Picturephone lines throughout a city.
will require some new kinds of test equipment,
although much of the equipment in use today
will still be usable. For example, a low-frequency
transmission measuring set will give a rough
idea of how a video facility is performing. But
it will be necessary to go beyond this and create
a video-frequency transmission measuring set.
Similarly, wideband versions of such instruments
as noise-measuring sets and variable frequency
oscillators will be needed. Most of these instru-
ments are similar in kind to voice-frequency
equipment; however, some new instruments will
be peculiar to the Picturephone system. These
include a video-image generator to serve as a
source of video test signals; a video monitor for
observing signals; an oscilloscope for observing
signal waveforms; and a delay measuring set, or
"echo-rating" set as it is sometimes called.
"Echo-rating" is a new concept. It is deter-
mined for a given facility by first measuring the
power in any echoes reflected from impedance
discontinuities in that facility. The powers of the
various echoes are then weighted, with the great-
est weight being assigned to the echoes that are
most delayed from the desired signal. The ratio of
the sum of weighted echo powers to the power of
the desired signal is called the echo rating. The
echo-rating test set will perform the rather com-
plex functions of measuring, comparing, and
weighting echoes, and will then display the re-
sult. After measuring individual sections of an Block diagram of the maintenance arrangements planned for
overall facility or connection with an echo-rating interoffice trunks in the No. 5 crossbar system. Audio facilities
set, it will be relatively simple to determine which are shown in black, and video facilities are shown in grail. Since
sections are the source of excessive echo signals. tandem and intertoll trunks terminate on both sides of the cen-
The echo-rating test set will be extremely use- tral office switching network (indicated here by the video and
ful in providing high-quality pictures. Along audio switches), test facilities must also have similar dual ac-
with all the other test equipment mentioned, it cess. Maintenance arrangements will include equipment for test-
is part of an overall plan to assure customers of ing wideband video signals and digital facilities such as the
trouble-free service as well. codecs that code (and decode) video signals into digital form.
May/June 1969 185
T HIS SPECIAL ISSUE of the Bell Laboratories
RECORD shows what we are doing to provide PIC-
teract with the computer through his TOUCH-
TUREPHONE® service. As the service becomes avail- As you have seen in this issue, a computer dis-
able to more and more people, new features will play capability has already been incorporated into
be developed to increase its versatility. For ex- Picturephone service, and this capability is being
ample, we are working on a method that will al- field-tested in the product trial with Westinghouse
low businessmen to see and read high-resolution Electric Corporation. Some future uses of the
i mages of drawings, sales literature, reports, and Picturephone set as a display device may well in-
the like. By using a slow-scan mode, which per- clude interactive computer graphics using a light-
mits high resolution with no increase in band- pen or special keyboard.
width (but at the sacrifice of being able to follow Many of the features mentioned in this issue
rapid motion), such graphics service can be pro- are being considered with a view toward improv-
vided over the Picturephone network. Hard copy ing the utility of Picturephone service for busi-
printout of picture images could be an added ness use. Picturephone services for other uses are
feature in such a service. being considered as well. For example, we'll be
A way to allow people to hold conferences via looking at special Picturephone sets for specific
three or more Picturephone sets is another es- applications. The present Mod II set, designed
sential need for business customers. And here too, primarily for desk-top application, will ultimately
work is in progress to add such a conferencing be joined by other models, such as wall models for
feature at the earliest practicable time. A voice- residential use. And it is not difficult to foresee
operated Picturephone conference system is now the eventual growth of booth service.
being evaluated in the laboratory. The system au- Color Picturephone service is an obvious sequel
tomatically distributes the Picturephone signal to our present development and hopefully com-
from the person speaking to all other listeners; patible with it. Broadcast color television sug-
the speaker sees the person who spoke last. Al- gests a general pattern for a system of color Pic-
though the system is intended primarily for face- turephone. However, the camera as used in color
to-face conferencing, it would not be limited to television today does not seem to be adaptable for
this use. It could be used for management presen- Picturephone. A Picturephone camera (1) must
tations that include charts and graphs, for ex- be able to operate satisfactorily under light of
ample, or for product or other pictorial displays. widely varying intensity and spectral content, (2)
Another possibility is that information generated should require little or no adjustment by the cus-
by a computer might be displayed on the sets of tomer, (3) should maintain its standards without
all conferees. In this case, each conferee could in- service adjustments for periods of many years,
186 Bell Laboratories Record
and (4) must especially give a good rendition of
facial skin tones. For these reasons, research and
exploratory development at Bell Laboratories are
now concentrating on color camera systems that
are simple, stable, and will work reliably in the
home or office environment.
Color perception by human beings has many
subjective characteristics. The colors we think we
see are often very different from the true color
of light reflected by objects in all the various con-
ditions of illumination. Fundamental research on
color perception at Bell Laboratories will, we
hope, yield greater basic understanding of this
Looking even further into the future, we can
i magine 3-D Picturephone images, or arrange-
ments whereby equipment could be attached to
deliver a print of whatever picture is on the
screen. It is easy to speculate about these and
other applications, but it is not so easy to find
answers to the many scientific and engineering
questions they imply. We nevertheless intend to
investigate all promising approaches, so that the
technology will be ready whenever the needs and
the economics are favorable to development.
In addition to the provision of new services we
must, of course, search constantly for ways to Research currently in progress at Bell Laboratories will lead
make Picturephone service cheaper. Further ex- eventually to the development of Picturephone service in color.
ploitation of integrated circuits will doubtless con-
tribute significantly in that direction. New cables
for the loop plant will make broadband transmis-
sion easier to accomplish. Methods of "bandwidth
reduction," in which only those elements of a pic-
ture are transmitted which change from frame to
frame, also look promising. Such a system has
been demonstrated by our research people. While
the terminal equipment needed to accomplish the
elimination of redundancy is, in its present form,
rather complicated, we are hoping that eventually
it can be made cheap enough to yield an overall
savings in the cost of transmission.
The coming of the Picturephone age will repre-
sent the maturing of a 1-MHz switched network.
Fortunately, as described in this issue, this net-
work can start as an "adjunct" to the network
now used for telephone services. It will use tele-
phone loops, trunks, and switching machines with
only relatively moderate changes and additions.
When the day comes, however, that Picturephone
represents a substantial part of our communica-
tion services, then its effect on the Bell System
plant will be profound. To get from now to then
is an exciting challenge to all parts of the Bell
System. To meet it and succeed will require hu-
man energy, capital funds, imagination, and wis-
dom in abundance. -J.P.M.
A voice-operated conference system, now being developed, will
increase the utility of Picturephone for business customers.
oping various transistor circuits
for the early electronic switching
systems. In 1960 he became Su-
pervisor of a group engaged in de-
signing data communication
equipment for use on ordinary tele-
phone facilities. He was named
Head of the Pulse Code Modula-
tion Repeater Department in 1962,
where his duties involved design-
ing a transcontinental system for
transmitting all kinds of informa-
tion by means of streams of high-
speed pulses. Mr. Dorros assumed
his present post in 1966.
Mr. Dorros attended the Massa-
chusetts Institute of Technology,
where he was awarded the S.B.
I. Dorros and S.M. degrees in electrical en-
gineering in 1956. He received the
Eng. Sc. D. (Doctor of Engineer-
Irwin Dorros (PI CTUREPHONE®) tem, the centralization and auto- ing Science) degree from Colum-
is Director of the Network Plan- mation of network operations, and bia University in 1962. Mr. Dorros
ning Center. His responsibilities planning for the toll network. is a member of the IEEE, Eta
include the systems engineering Mr. Dorros joined Bell Labs in Kappa Nu, Tau Beta Pi, and
aspects of the Picturephone sys- 1956. His first work was on devel- Sigma Xi.
Claude G. Davis (Getting the Pic- System's experimental communi-
ture) is Director of the Telephone cations satellite program. He be-
Laboratory at Bell Labs' Holmdel, came Head of a department de-
N. J., location. His organization veloping customer radio systems
develops new kinds of telephone in 1962, and Head of the Sub-
instruments for use by customers; scriber Loop Systems Department
the Mod II Picturephone set was in 1964. He was appointed Direc-
one of its products. tor of the Subscriber Systems Lab-
Mr. Davis joined Bell Labs in oratory in 1966, and assumed his
1950, and his early work concerned present position last year.
development of exchange and toll Born in Beech Grove, Indiana,
cable. Later he specialized in de- Mr. Davis graduated from high
velopment of transmission sys- school in Ashtabula, Ohio. He re-
tems and worked on Pulse Code ceived the B.S. degree in electrical
Modulation (PCM) and Time As- engineering from Case Institute of
signment Speech Interpolation Technology in 1950, and the M.S.
( TASI). In 1961 he became Head degree in math from Stevens In-
of a department responsible for stitute of Technology in 1960. Mr.
repeater design and data analysis Davis is a member of the IEEE
in the TELSTAR® project, the Bell and Eta Kappa Nu.
C. G. Davis
James R. Harris (co-author Video Director of the Data Systems En-
Service for Business) is Director gineering Center in 1961, and took
of the Customer Switching Engi- over his present position in 1965.
neering Center, which is responsi- Before coming to Bell Labs,
ble for engineering studies of PBX Mr. Harris was with the Chesa-
and key telephone systems, some peake and Potomac Telephone
aspects of coin telephone service Company, first as a toll central of-
i mprovement, speech processing, fice repairman and later in equip-
customer switching systems, and ment engineering.
planning of new network arrange- Mr. Harris received the B.S. de-
ment for government communica- gree in physics from the Univer-
tions. sity of Richmond in 1941, and the
Upon joining Bell Labs in 1942 M.E.E. degree from the Polytech-
Mr. Harris developed airborne ra- nic Institute of Brooklyn in 1948.
diotelephone and navigation sets. He is a member of the IEEE and
In 1950 he joined a group develop- a past member of the Administra-
ing transistors and digital tran- tive Committee of the Institute's
sistor circuits. He joined the TRA- Group on Electronic Computers.
DIC (Transistor Airborne Digital He is also a member of Phi Beta
Computer) project when it was Kappa and Sigma Xi.
formed in 1951. In 1956 Mr. Har-
ris was appointed Head of a de-
partment concerned with data pro-
cessing. Two years later he turned
to exploratory work on data com-
munications. He was appointed
J. R. Harris
Robert D. Williams (co-author come Director of a new Bell Labs
Video Service for Business) is switching development center to
Director of the Customer Tele- be built in Denver, Colorado, where
phone Systems Laboratory. He is he will be responsible for the de-
responsible for development of velopment of telephone communi-
PBX's, key telephone systems, cation facilities installed by Bell
telephone answering systems, au- System companies on customers'
tomatic call distributors, and pri- premises, such as key systems and
vate telephone systems. PBX's.
Mr. Williams came to Bell Labs Mr. Williams received the B.S.
in 1946 and joined the trial instal- degree in electrical engineering
lation group, where he worked on from the Case School of Applied
the first installation of the No. 5 Science in 1945. He is a member
crossbar switching system. He was of the IEEE, Tau Beta Pi, Eta
later concerned with developing Kappa Nu, Theta Tau, and Pi
the 740E and 756A PBX's and Delta Epsilon.
special systems such as recorded
telephone-dictation equipment and
the Civil Air Raid Warning Sys-
tem. He also worked on develop-
ing the No. 101 ESS, an electronic
PBX. Mr. Williams became Head
of the PBX Development Depart-
ment in 1961, and took over his
present post last year. He will be- R. D. Williams
May/June 1969 189
Frank A. Korn (co-author Choos- Mr. Korn was responsible for ex-
ing the Route) is Director of the ploratory development of a new
Local Crossbar Switching Labora- dial switching system using elec-
tory at Bell Labs' location in the tronic devices and intended for use
Western Electric Company Works in small communities. In 1947 he
at Columbus, Ohio. He has been assumed responsibility for all cir-
deeply involved with No. 5 cross- cuit development of a new dial
bar switching since its inception switching system-No. 5 crossbar.
in 1945, and his present responsi- He was named Director of Switch-
bilities include all development ing Systems Development in 1952;
work being done to keep this with responsibility for develop-
"workhorse" system up to date ment work on all local dial central
and extend its usefulness. offices and PBX's. When the Co-
Mr. Korn has been with Bell lumbus Laboratory was organized
Labs since its incorporation in in 1958, Mr. Korn was appointed
1925. He came to the Bell System its Director and charged with get-
in 1920 as a member of the Engi- ting the new facility going. He
neering Department of the West- took over his present post in 1963
ern Electric Company, which be- when the Columbus facility was
came BTL five years later. Ever expanded. Mr. Korn was a mem-
since then his work has concerned ber of the RECORD's Editorial
dial switching systems. He first Board from 1952 to 1959.
worked on the panel and step-by- Active in community affairs, Mr.
step systems. In 1933 he joined a Korn is a member of the Colum-
group responsible for fundamental bus Area Chamber of Commerce.
planning of crossbar switching He is also a member of the Ad-
systems, including No. 1 crossbar, visory Committee to the Columbus
crossbar tandem, and No. 4 toll. Area Technical School, the Advis-
F. A. Korn During the war his efforts were ory Board of the St. Ann's Hos-
diverted to military projects, in- pital in Columbus, and the Board
cluding the design of airborne nav- of Directors of the Ohio State
igation radar and bombing sys- University Research Foundation.
tems. He was named a Fellow of the
For a short time after the war IEEE last year.
Alistair E. Ritchie (co-author pointed Special Systems Engineer
Choosing the Route) is Director in charge of certain military com-
of the Toll Switching Engineering munications and government pro-
Center, which is responsible for jects. He became Systems Plan-
engineering studies of toll switch- ning Engineer in 1955 and was
ing systems. engaged in studies of line concen-
Mr. Ritchie joined Bell Labs in trators and the original applica-
1937 as a member of the testing tion of TOUCH-TONE® dialing. In
laboratory in the switching devel- 1958 he became Director of Switch-
opment organization. In this ca- ing Systems Engineering, where
pacity he worked on the testing he was responsible for engineer-
program for the original No. 1 ing planning of electro/mechanical
and No. 4 crossbar systems. After switching systems, and in 1965 he
instructing in Bell Labs' School for assumed his present position.
War Training, Mr. Ritchie joined Mr. Ritchie received the B.A.
a group planning and teaching and M.A. degrees in physics in
courses in design of switching cir- 1935 and 1937, respectively, from
cuits. He taught a graduate course Dartmouth College. He is a senior
in the principles and design of member of the IEEE. He is co-
switching circuits at MIT in 1950- author, with W. Keister and S.
1951. Later he was concerned with H. Washburn, of The Design of
the planning of traffic measuring Switching Circuits, which is a
equipment, and in 1953 was ap- standard text on the subject.
Bell Laboratories Record
A. E. Ritchie
D. W. Nast I. Welber
David W. Nast (co-author Trans- College of Engineering in 1957. His early assignments included
mission Across Town or Across He received the Professional Elec- circuit design, systems analysis,
the Country) is Director of the trical Engineer's degree from Co- and field testing of an automatic
Transmission Facilities Planning lumbia in 1964. He is a member protection system for microwave
Center. His responsibilities include of the IEEE, Eta Kappa Nu, Phi radio. He later did system analy-
engineering planning of wire, ra- Kappa Phi, and Tau Beta Pi. sis and design work on the Time
dio, and satellite transmission fa- Assignment Speech Interpolation
cilities. (TASI) system. In 1960 he was
Since joining Bell Labs in 1953 appointed Head of the Ground Sta-
Mr. Nast has specialized in sys- tion Design Department, in which
tems engineering in such fields as post he was responsible for over-
exchange transmisssion, pulse all systems analysis, ground com-
transmission studies, and wide- Irwin Welber (co-author Trans- munication equipment, and tech-
band data transmission. He was mission Across Town or Across nical planning with foreign
appointed Head of the Broadband the Country) is Director of the participants on project TELSTAR®.
Systems Studies Department in Overseas and Microwave Trans- During the early Telstar experi-
1964. In 1966 he became Head of mission Laboratory. His organi- ments he was in charge of oper-
the PICTUREPHONE® Engineering zation is responsible for the ations at the ground station in
Department, responsible for the development of transoceanic sub- Andover, Maine. He moved up to
technical planning for Picture- marine cable systems, waveguide his present position in 1965.
phone service. He moved to his transmission, high-frequency ra- Mr. Welber received the B.S. de-
present position last year. dio, and digital transmission on gree in electrical engineering from
Mr. Nast received the B.E.E. de- existing radio systems. Union College in 1948 and his
gree from Cornell University in Since coming to Bell Labs in M.E.E. from Rensselaer Polytech-
1953, and the M.S. degree in elec- 1950, Mr. Welber has specialized nic Institute in 1950. He is a mem-
trical engineering from Newark in work on transmission systems. ber of the IEEE and Sigma Xi.
Frederick T. Andrews, Jr. (co-
author Connecting the Customer)
is Director of the Loop Systems
Laboratory. He is responsible for
development work on the "loops"
that connect customers' telephones
to their local switching offices.
Upon joining Bell Labs in 1948
Mr. Andrews worked in switching
research on line concentrators and
magnetic logic devices, and in 1955
he became a Supervisor in trans-
mission systems development. En-
gaged in exploratory development
of Pulse Code Modulation (PCM)
transmission, he was responsible
for planning and circuit develop- F. T. Andrews, Jr.
ment of portions of the terminals
and line repeaters for the experi-
mental forerunner of the first com- Henry Z. Hardaway (co-author
mercial PCM system. In 1958 he Connecting the Customer) is Di-
became Head of the Transmission rector of the Exchange Plant Sys-
Systems Engineering Department, tems Engineering Center. He di-
and was responsible for transmis- rects engineering studies of new
sion objectives and maintenance in communications cable and wire fa-
the telephone and data fields. He cilities, inductive interference, and
was appointed Director of the outside plant maintenance. In-
Transmission Systems Engineer- cluded is the responsibility for ex-
ing Center in 1962, and Director change transmission requirements,
of the Military Communications station set requirements, special
Systems Engineering Center in services requirements, and studies
1966. He took over his present po- of the application of electronics to
sition last year. the exchange plant. He is also re-
Mr. Andrews received the B.S. sponsible for studies leading to
degree in electrical engineering the application of electronic com-
from Pennsylvania State Univers- puter techniques as tools for Bell
ity in 1948, was a member of the System operating telephone com-
first group to enroll in Bell Lab- pany engineers to use in solving
oratories' Communications Devel- their engineering and planning
opment Training Program, and problems in the exchange plant.
has done graduate work in math- Upon joining Bell Labs in 1942
ematics at Rutgers University. He Mr. Hardaway engaged in equip-
is active in the IEEE as a mem- ment design work on various mil-
ber of the Wire Communications itary projects, including airborne
Committee, where he heads a task and submarine radar equipment
force on telephone measurement. and navigation equipment. In 1955
As Vice Chairman of a Study he became Head of a department
Group of the Committee Consul- in outside plant systems engineer- H. Z. Hardaway
tatif International Telegraphique ing. In 1963 he was appointed Di-
and Telephonique, he is concerned rector of Outside Plant Systems
with transmission objectives and Engineering, directing the plan-
local transmission standards as re- ning of new cable and wire facil-
lated to planning the world-wide ities for the Bell System and con-
commercial telephone network. ducting other studies. Last year
he moved to his present post.
Mr. Hardaway received the B.S.
degree in mechanical engineering
from the State University of Iowa
in 1940. He is a member of the
American Society of Mechanical
Engineers and the American Ord-
1 92 Bell Laboratories Record
Sture O. Ekstrand ( Devices- processing of electron tubes. From
The Hardware of Progress) is Di- 1945 to 1955 Mr. Ekstrand super-
rector of the Semiconductor De- vised electrical and mechanical de-
vice and Electron Tube Labora- velopment of certain types of elec-
tory at Reading, Pennsylvania. He tron tubes, and was a consultant
is responsible for development of to BTL groups doing military
semiconductor devices such as di- work. In 1955 he became Head of
odes and microwave transistors, a department at Bell Labs' loca-
silicon integrated circuits, and elec- tion in Allentown, Pa., where he
tron tubes. was responsible for developing
After coming to Bell Labs in certain chemical processes, struc-
1926 Mr. Ekstrand specialized in tures for semiconductor devices
the design of mechanical struc- and electron tubes, and for applied
tures for test fixtures and ma- mechanics studies. He moved to
chines, as well as various kinds of the Reading Laboratory in 1957,
telephone and recording appara- and became its Director in 1960.
tus. In 1935 he moved to the Elec- Mr. Ekstrand received the B.S.
tron Tube Laboratory, where he degree in electrical engineering
engaged in development of all from Cooper Union in 1935. He is
types of electron tubes for both a member of AAAS and a Fellow
Bell System and military applica- of the IEEE. He is also a mem-
tions. In 1941 and 1942 he was a ber of the Joint Electron Device
production engineer with the West- Engineering Council, the Elec-
ern Electric Company; then he re- tronic Industries Association, and
turned to BTL and supervised a the United States of America
group responsible for design and Standards Institute.
S. O. Ekstrand
Albert E. Spencer, Jr. ( Mainte- He later supervised one of several
nance-Keeping The System In groups responsible for planning
Trim) is Director of the Local a global military communication
Switching Engineering Center. His system. In 1962 he was appointed
organization conducts studies in Head of the Data Switching Engi-
the local switching field and es- neering Department, responsible
tablishes objectives and require- for objectives and requirements
ments for local switching systems. for a store-and-forward data com-
Mr. Spencer joined Bell Labs in munication system. He has held
1951. After assignments in the de- his present post since 1965.
sign of circuits for transmission Mr. Spencer received the B.S.
systems and a secure voice com- degree in electrical engineering
munication system, he supervised from the Drexel Institute of Tech-
initial design work on the time- nology in 1951. He is a member of
division switch unit for the No. the IEEE, the AAAS, Tau Beta
101 Electronic Switching System. Pi, and Eta Kappa Nu.
A. E. Spencer, Jr.
May/June 1969 1 93